Rendezvous with Cassidoo: solutions to interview questions of the week from the [rendezvous with cassidoo newsletter](https://buttondown.email/cassidoo)

a-rendezvous-with-cassidoo.md

Rendezvous with Cassidoo Solutions

Solutions to the interview question of the week from the rendezvous with cassidoo newsletter

Solutions in the following languages:

• TypeScript
• Elixir

Inspired and forked from jda0

p155.ts

/**
 *
 * Sort an array of strings based on the number of distinct characters that
 * occur in the word (followed by the length of the word).
 *
 * $ charNumSort([“Bananas”, “do”, “not”, “grow”, “in”, “Mississippi”])
 * $ do in not Mississippi Bananas grow
 *
 *
 */

const charNumSort = (input: Array<string>) =>
  input
    .sort((first, second) => {
      // use Set() to find unique char count
      const compare = [...new Set(first)].length - [...new Set(second)].length;

      return compare ? compare : second.length - first.length;
    })
    .join(" ");

console.log(charNumSort(["Bananas", "do", "not", "grow", "in", "Mississippi"]));

// https://codesandbox.io/s/modest-sanderson-wxs33?file=/src/index.ts

p157.ts

/**
 *
 * Given an array of random integers, move all the zeros in the array to the end
 * of the array. Try to keep this in O(n) time (or better)! Example:
 * $ moveZeros([1, 2, 0, 1, 0, 0, 3, 6])
 * $ [1, 2, 1, 3, 6, 0, 0, 0]
 *
 */

const moveZeros = (arr: Array<number>) => {
  let numberOfZeroes = 0;
  const result = arr.reduce((agg, curr) => {
    curr ? agg.push(curr) : numberOfZeroes++;
    return agg;
  }, [] as number[]);

  return [...result, ...Array(numberOfZeroes).fill(0)];
};

console.log(moveZeros([1, 2, 0, 1, 0, 0, 3, 6]));

// https://codesandbox.io/s/misty-forest-pxdog?file=/src/index.ts

p158.ts

/**
 *
 * Given a string s and a character c, return the number of occurrences of c in
 * s. Example:
 *
 * $ numChars(‘oh heavens’, ‘h’)
 * $ 2
 *
 */

const numChars = (input: string, char: string) =>
  /**
   *
   * yay regular expressions! global flag since we wanna count *all* instances
   * return 0 in case of no matches
   *
   */
  (input.match(RegExp(char, "g")) || []).length;

console.log(numChars("oh heavens", "h"));

// https://codesandbox.io/s/mystifying-swirles-8h5it?file=/src/index.ts

p159.ts

/**
 *
 * Given an array of numbers that represent stock prices (where each number is
 * the price for a certain day), find 2 days when you should buy and sell your
 * stock for the highest profit. Example:
 *
 * $ stockBuySell([110, 180, 260, 40, 310, 535, 695])
 * $ “buy on day 4, sell on day 7”
 *
 */

const stockBuySell = (prices: Array<number>) =>
  `buy on day ${prices.indexOf(Math.min(...prices)) + 1}\
, sell on day ${prices.indexOf(Math.max(...prices)) + 1}`;

// A much faster way.
// The earlier one is ~88% slower: https://jsbench.me/54keiiwuvy/1
const stockBuySellReduce = (prices: Array<number>) => {
  const minMax = prices.reduce(
    (agg, curr, index, arr) => {
      if (curr < arr[agg.min]) agg.min = index;
      else if (curr > arr[agg.max]) agg.max = index;
      return agg;
    },
    { min: 0, max: 0 },
  );
  return `buy on day ${minMax.min + 1}, sell on day ${minMax.max + 1}`;
};

console.log(stockBuySell([110, 180, 260, 40, 310, 535, 695]));
console.log(stockBuySellReduce([110, 180, 260, 40, 310, 535, 695]));

// https://codesandbox.io/s/sharp-jepsen-8npl1?file=/src/index.ts

p163.ts

/**
 *
 * Given an array of people objects (where each person has a name and a number
 * of pizza slices they’re hungry for) and a number for the number of slices
 * that the pizza can be sliced into, return the number of pizzas you need to
 * buy.
 *
 * $ arr = [
 * $   { name: Joe, num: 9 },
 * $   { name: Cami, num: 3 },
 * $   { name: Cassidy, num: 4 },
 * $ ]
 * $ gimmePizza(arr, 8)
 * $ 2
 * $ // 16 slices needed, pizzas can be sliced into 8 pieces,
 * $ // so 2 pizzas should be ordered
 *
 */

type TPeopleSlicesMap = {
  name: string;
  num: number;
};
const gimmePizza = (arr: Array<TPeopleSlicesMap>, maxSlices: number) => {
  const totalSlices = arr.reduce((total, { num }) => {
    return (total += num);
  }, 0);
  return Math.ceil(totalSlices / maxSlices);
};

const inputMap = [
  { name: "Joe", num: 9 },
  { name: "Cami", num: 3 },
  { name: "Cassidy", num: 4 },
];
console.log(gimmePizza(inputMap, 8));

// https://codesandbox.io/s/young-darkness-61nq3?file=/src/index.ts

p171.ts

/**
 *
 * Given a positive integer n, write a function that returns true if it is a
 * perfect square and false otherwise. Don’t use any built-in math functions
 * like sqrt. Hint: Use binary search!
 *
 * Examples:
 * $ perfectSquare(25)
 * $ true
 *
 * $ perfectSquare(10)
 * $ false
 *
 */

const isPerfectSquare = (input: number) => {
  const binarySearchPerfectSquare = (
    input: number,
    start: number,
    end: number,
  ): number | boolean => {
    if (start > end) return false;

    // mid value, parsed to an int using bitwise operator
    const mid = ((start + end) / 2) >> 0;
    if (mid * mid < input)
      return binarySearchPerfectSquare(input, mid + 1, end);
    if (mid * mid > input)
      return binarySearchPerfectSquare(input, start, mid - 1);
    // mid*mid === input, perfect square!
    return true;
  };
  return binarySearchPerfectSquare(input, 1, input);
};

console.log(isPerfectSquare(25));
console.log(isPerfectSquare(10));

// https://codesandbox.io/s/relaxed-pine-yofdz?file=/src/index.ts

p172.ts

/**
 *
 * Given an array of integers and a target value, return the number of pairs of
 * array elements that have a difference equal to a target value.
 *
 * Example:
 * $ arrayDiff([1, 2, 3, 4], 1)
 * $ 3 // 2 - 1 = 1, 3 - 2 = 1, and 4 - 3 = 1
 *
 */

const arrayDiff = (arr: Array<number>, target: number) => {
  let count = 0,
    flag = false;

  arr
    .sort()
    .reverse()
    .forEach((baseNum, i, reverseSortedArr) => {
      if (i === arr.length) return;
      flag = false;
      reverseSortedArr.slice(i + 1).forEach((num, j) => {
        // arr is sorted, so we won't get the target diff again
        if (flag) return;
        if (j === reverseSortedArr.length) return;
        if (baseNum - num === target) {
          count += 1;
          flag = true;
        }
      });
    });
  return count;
};

console.log(arrayDiff([1, 2, 3, 4], 1));

// https://codesandbox.io/s/cool-satoshi-84ku4?file=/src/index.ts

p176.ts

/**
 *
 * You’re given a string of characters that are only 2s and 0s. Return the index
 * of the first occurrence of “2020” without using the indexOf (or similar)
 * function, and -1 if it’s not found in the string.
 *
 * Example:
 * $ find2020(‘2220000202220020200’)
 * $ 14
 *
 */

const find2020 = (input: string) => {
  let index = -1;
  input.split("").reduce(
    (_shouldBe2020, _curr, i) => {
      const next4 = input.slice(i, i + 4);
      if (next4 === "2020") index = i;
      return next4;
    },
    input.slice(0, 4),
  );
  return index;
};

// https://codesandbox.io/s/sharp-mountain-wddiy?file=/src/index.ts

p187.ts

/**
 *
 * Given a rowIndex, return an array of the values in that row of Pascal’s
 * Triangle.
 *
 */

const getCurrentRow = (previousRow: Array<number>): Array<number> => {
  return Array.from(Array(previousRow.length + 1)).map((_, i) => {
    if (i === 0) return 1;
    else if (i === previousRow.length) return 1;
    else return previousRow[i - 1] + previousRow[i];
  });
};

const getPascalRow = (index: number): Array<number> => {
  if (index === 0) return [1];
  return getCurrentRow(getPascalRow(index - 1));
};

console.log(getPascalRow(0)); // [1]
console.log(getPascalRow(1)); // [1, 1]
console.log(getPascalRow(2)); // [1, 2, 1]
console.log(getPascalRow(3)); // [1, 3, 3, 1]
console.log(getPascalRow(4)); // [1, 4, 6, 4, 1]

// https://codesandbox.io/s/heuristic-wood-qzzbd?file=/src/index.ts

p195.ts

/**
 *
 * Given an integer n, return true if n^3 and n have the same set of digits.
 * Example:
 *
 * $ sameDigits(1) // true
 * $ sameDigits(10) // true
 * $ sameDigits(251894) // true
 * $ sameDigits(251895) // false
 *
 */

const INPUTS = [1, 10, 251894, 251895];

const getUniqueDigitsAsString = (input: number) =>
  [...new Set(input.toString().split("").sort())].join();

const sameDigits = (input: number) => {
  const inputDigits = getUniqueDigitsAsString(input);
  const cubeDigits = getUniqueDigitsAsString(Math.pow(input, 3));
  return inputDigits === cubeDigits;
};

INPUTS.forEach((input) => console.log(sameDigits(input)));
// true, true, true, false

// https://codesandbox.io/s/cold-cdn-85qcb?file=/src/index.ts

p198.ts

/**
 *
 * Given a list, return a list of all its prefixes in ascending order of their
 * length. You’re essentially implementing the inits function in Haskell!
 *
 * Example:
 * $ inits([4, 3, 2, 1])
 * $ [[], [4], [4,3], [4,3,2], [4,3,2,1]]
 *
 * $ inits([144])
 * $ [[], [144]]
 *
 */

const INPUT = [4, 3, 2, 1];

const inits = (input: Array<number>) =>
  input.reduce(
    (arr, curr, index) => {
      arr.push([...arr[index], curr]);
      return arr;
    },
    [[]] as number[][],
  );

console.log(inits(INPUT));

// https://codesandbox.io/s/determined-swanson-qn27b?file=/src/index.ts

p200.ts

/**
 *
 * Given a direction and a number of columns, write a function that outputs an
 * arrow of asterisks (see the pattern in the examples below)!
 *
 * Example:
 *
 * $ printArrow('right', 3)
 * Output:
 *
 *
 *
 *
 *
 *
 *
 * $ printArrow('left', 5)
 * Output:
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

const printArrow = (direction: "right" | "left", len: number) => {
  Array.from(Array(2 * (len - 1) + 1)).forEach((_, index) => {
    let numSpaces;
    if (direction === "right") {
      numSpaces = index > len - 1 ? 2 * len - 2 - index : index;
    } else {
      numSpaces = len - (index > len - 1 ? 2 * len - 1 - index : index + 1);
    }
    console.log(`${" ".repeat(numSpaces)}*`);
  });
};

// https://codesandbox.io/s/gifted-perlman-0yvo0?file=/src/index.ts

p202.ts

const LINE = "█".repeat(10);
const PRIDE_COLORS = [
  "#e40303",
  "#ff8c00",
  "#ffed00",
  "#008026",
  "#004dff",
  "#750787",
];

const PrideFlag = () => {
  PRIDE_COLORS.forEach((color) => {
    console.log(`%c${LINE}`, `color: ${color}`);
  });
};

PrideFlag();

// https://codesandbox.io/s/blissful-leavitt-86k1s?file=/src/index.ts

p211.ts

/**
 *
 * Write a function to find the longest common prefix string in an array of
 * strings.
 *
 * Example:
 *
 * $ longestPrefix(["cranberry","crawfish","crap"])
 * $ "cra"
 *
 * $ longestPrefix(["parrot", "poodle", "fish"])
 * $ ""
 *
 */

function longestPrefix(input: Array<string>) {
  let result = "";

  input[0].split("").reduce((prefix, currentLetter) => {
    const isPrefixValid = input.every((word) => word.startsWith(prefix));
    if (isPrefixValid) {
      result = prefix;
      return `${prefix}${currentLetter}`;
    }
    return result;
  }, "");
  return result;
}

// https://codesandbox.io/s/heuristic-dan-pl0nn?file=/src/index.ts

p217.ts

/**
 *
 * An “odious number” is a non-negative number that has an odd number of 1s in
 * its binary expansion. Write a function that returns true if a given number is
 * odious.
 *
 * Example:
 *
 * $ isOdious(14)
 * $ true
 *
 * $ isOdious(5)
 * $ false
 *
 */

const isOdious = (input: number) =>
  (input.toString(2).match(/1/g) ?? []).length % 2 === 1;

// https://codesandbox.io/s/admiring-poitras-8l6sd?file=/src/index.ts

p218.ts

/**
 *
 * Given an array of objects A, and an array of indexes B, reorder the objects
 * in array A with the given indexes in array B.
 *
 * Example:
 *
 * let a = [C, D, E, F, G, H]; let b = [3, 0, 4, 1, 2, 5];
 *
 * $ reorder(a, b) // a is now [D, F, G, C, E, H]
 *
 */

const reorder = (
  a: Array<Record<string, unknown> | string>,
  b: Array<number>,
) =>
  [...Array(a.length)].reduce((res, _, index) => {
    res[b[index]] = a[index];
    return res;
  }, []);

// https://codesandbox.io/s/agitated-bash-tmu25?file=/src/index.ts

p259.ex

defmodule RWC_259 do
  @doc """
  Given an integer n, count the total number of 1 digits appearing in all
  non-negative integers less than or equal to n.

  Example:

  > numberOfOnes(14)
  > 7 // 1, 10, 11, 12, 13, 14
  """
  defp count_one_recursively(input, count) when input == 1, do: count + 1

  defp count_one_recursively(input, count) do
    input
    |> Integer.to_string()
    |> String.split("")
    |> Enum.count(&(&1 == "1"))
    |> then(fn x ->
      case x > 0 do
        true ->
          count_one_recursively(input - 1, count + x)

        _ ->
          count_one_recursively(input - 1, count)
      end
    end)
  end

  def number_of_ones(input) do
    input
    |> count_one_recursively(0)
    |> IO.puts()
  end
end

RWC_259.number_of_ones(14)

p270.ex

defmodule RWC_270 do
  @doc """
  Let’s say you have n doors that start out as closed. With the first pass
  across the doors, you toggle every door open. With the second pass, you toggle
  every second door. With the third, every third door, and so on. Write a
  function that takes in an integer numberOfPasses, and returns how many doors
  are open after the number of passes.

  Example:

  let n = 7 let numberOfPasses = 3

  > passDoors(n, numberOfPasses)
  > 4

  // Explanation: // 0 means open, 1 means closed // Initial: 1 1 1 1 1 1 1 //
  Pass 1:  0 0 0 0 0 0 0 // Pass 2:  0 1 0 1 0 1 0 // Pass 3:  0 1 1 1 0 0 0
  """
  @spec pass_doors(n :: non_neg_integer, number_of_passes :: non_neg_integer) ::
          non_neg_integer
  def pass_doors(n, number_of_passes) do
    1..number_of_passes
    # duplicate with n+1 because map_every/3 starts from first elem indexed 0
    # open => true, closed => false
    |> Enum.reduce(List.duplicate(false, n + 1), fn nth, doors ->
      Enum.map_every(doors, nth, &(not &1))
    end)
    # ignore the extra door we added at the start
    |> Enum.drop(1)
    |> Enum.count(& &1)
  end
end

RWC_270.pass_doors(7, 3)

p281.ex

defmodule RWC_281 do
  @doc """
  Given an array of integers arr and an integer n, return a subarray of arr of
  length n where the sum is the largest.

  Make sure you maintain the order of the original array, and if n is greater
  than arr.length, you can choose what you want to return.

  > maxSubarray([-4,2,-5,1,2,3,6,-5,1], 4)
  > [1,2,3,6]

  > maxSubarray([1,2,0,5], 2)
  > [0,5]
  """

  def maxSubarray(input, size) do
    input
    |> Enum.chunk_every(size, 1, :discard)
    |> Enum.max_by(&Enum.sum(&1))
  end
end

IO.inspect(RWC_281.maxSubarray([-4, 2, -5, 1, 2, 3, 6, -5, 1], 4))
IO.inspect(RWC_281.maxSubarray([1, 2, 0, 5], 2))

p282.ex

defmodule RWC_282 do
  @doc """
  Given a number, sum every second digit in that number.

  Example:

  > sumEveryOther(548915381)
  > 26 // 4+9+5+8

  > sumEveryOther(10)
  > 0

  > sumEveryOther(1010.11)
  > 1 // 0+0+1
  """

  def sumEveryOther(input) do
    input
    |> to_string()
    |> String.graphemes()
    |> List.delete_at(0)
    |> Enum.filter(&(&1 !== "."))
    |> Enum.take_every(2)
    |> Enum.map(&String.to_integer/1)
    |> Enum.sum()
  end
end

p284.ex

defmodule RWC_284 do
  @doc """
  You are given a list of positive integers which represents some range of
  integers which has been truncated. Find the missing bits, insert ellipses to
  show that that part has been truncated, and print it. If the consecutive
  values differ by exactly two, then insert the missing value.

  Examples:

  > missingBits([1,2,3,4,20,21,22,23])
  > "[1,2,3,4,...,20,21,22,23]"

  > missingBits([1,2,3,5,6])
  > "[1,2,3,4,5,6]"

  > missingBits([1,3,20,27])
  > "[1,2,3,...,20,...,27]"
  """

  def missingBits(input) do
    input
    |> Enum.with_index()
    |> then(fn input_with_index ->
      input_with_index
      |> Enum.reduce([], fn {num, index}, acc ->
        {next_num, _} = Enum.at(input_with_index, index + 1, {num, nil})

        case next_num - num do
          # Last index
          0 -> [num | acc]
          1 -> [num | acc]
          # When step is exactly two
          2 -> [num + 1, num | acc]
          _ -> ["...", num | acc]
        end
      end)
      |> Enum.reverse()
      |> Enum.join(",")
      |> then(&"[#{&1}]")
    end)
  end
end

p285.ex

defmodule RWC_285 do
  @doc """
  Given a positive integer, generate an array in which every element is an array
  that goes from 1 to the index of that array.

  Example:

  > generateArrays(4)
  > [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4]]

  > generateArrays(1)
  > [[1]]
  """

  def generateArrays(input) do
    1..input
    |> Enum.to_list()
    |> Enum.map(&Enum.to_list(1..&1))
  end
end

p286.ex

defmodule RWC_286 do
  @doc """
  Spreadsheet programs often use the A1 Reference Style to refer to columns.
  Given a column name in this style, return its column number.

  Examples of column names to their numbers:

  A -> 1 B -> 2 C -> 3 // etc Z -> 26 AA -> 27 AB -> 28 // etc AAA -> 703
  """

  def get_weight(char, power) do
    char
    |> String.to_charlist()
    |> hd()
    # A => 65, B => 66, so on...
    |> then(&(&1 - 64))
    |> then(&(&1 * 26 ** power))
  end

  def recusively_get_weight([{char, index}]), do: get_weight(char, index)

  def recusively_get_weight([left | rest]),
    do: recusively_get_weight([left]) + recusively_get_weight(rest)

  def get_column_number(input) do
    input
    |> String.split("", trim: true)
    |> Enum.reverse()
    |> Enum.with_index()
    |> recusively_get_weight()
  end
end

p287.ex

defmodule RWC_287 do
  @doc """
  Print the digits 0 through 100 without using the characters 1, 2, 3, 4, 5, 6,
  7, 8, or 9 in your code. Get creative!
  """

  def print_digits() do
    hundred =
      "d"
      |> to_charlist()
      |> hd()

    zero =
      [hundred - hundred]
      |> hd()

    zero..hundred
    |> Enum.join(", ")
  end
end

p288.ex

defmodule RWC_288 do
  @doc """
  Given a string of parenthesis, return the number of parenthesis you need to
  add to the string in order for it to be balanced.

  Examples:

  > numBalanced(`()`)
  > 0

  > numBalanced(`(()`)
  > 1

  > numBalanced(`))()))))()`)
  > 6

  > numBalanced(`)))))`)
  > 5
  """

  def num_balanced(input) do
    input
    |> String.split("", trim: true)
    |> Enum.frequencies()
    |> Map.values()
    |> then(
      &case &1 do
        [only_one_kind] -> only_one_kind
        [one, other] -> abs(one - other)
      end
    )
  end
end

p289.ex

defmodule RWC_289 do
  @doc """
  Given a list of numbers, return all groups of repeating consecutive numbers.

  Examples:

  > repeatedGroups([1, 2, 2, 4, 5])
  [[2, 2]]

  > repeatedGroups([1, 1, 0, 0, 8, 4, 4, 4, 3, 2, 1, 9, 9])
  [[1, 1], [0, 0], [4, 4, 4], [9, 9]]
  """

  def chunk_repeats([head | rest]), do: chunk_repeats(rest, [[head]])
  def chunk_repeats([], done), do: done

  def chunk_repeats([head | rest], [
        [head | head_repeated] | previously_repeated
      ]),
      do:
        chunk_repeats(rest, [
          [head | [head | head_repeated]] | previously_repeated
        ])

  def chunk_repeats([head | rest], previously_repeated),
    do: chunk_repeats(rest, [[head] | previously_repeated])

  def repeated_groups(input) do
    input
    |> chunk_repeats()
    |> Enum.reverse()
    |> Enum.filter(&(length(&1) > 1))
  end
end

p300.ex

defmodule RWC_300 do
  @doc """
  Write a function to find out whether the binary representation of a number is
  palindrome or not.

  Example:

  > binaryPal(5) > true

  > binaryPal(10) > false
  """

  def binary_pal(input) do
    input
    |> Integer.to_charlist(2)
    |> List.to_string()
    |> then(fn digits ->
      digits
      |> String.reverse()
      |> then(
        &case &1 do
          ^digits -> true
          _ -> false
        end
      )
    end)
  end
end

p301.ex

defmodule RWC_301 do
  @doc """
  Given a string, calculate the score that it would get in a game of Scrabble.
  For extra credit, try verifying if the string is a valid word, or take into
  account premium squares!

  Scoring and example:

  1 point: E, A, I, O, N, R, T, L, S, U 2 points: D, G 3 points: B, C, M, P 4
  points: F, H, V, W, Y 5 points: K 8 points: J, X 10 points: Q, Z

  > scrabbleScore('FIZZBUZZ')
  > 49
  """

  @score_map %{
    "EAIONRTLSU" => 1,
    "DG" => 2,
    "BCMP" => 3,
    "FHVWY" => 4,
    "K" => 5,
    "JX" => 8,
    "QZ" => 10
  }

  def scrabble_score(input) do
    input
    |> String.split("", trim: true)
    |> Enum.reduce(0, fn letter, score ->
      @score_map
      |> Map.keys()
      |> Enum.find(&String.contains?(&1, letter))
      |> then(&Map.get(@score_map, &1))
      |> Kernel.+(score)
    end)
  end
end

p303.ex

defmodule RWC_303 do
  @doc """
  Given an array of people objects (where each person has a name and a number of
  pie pieces they’re hungry for) and a number for the number of pieces that the
  pie can be cut into, return the number of pies you need to buy.

  Example:

  iex>
  ...>  arr = [
  ...>    %{ name: Joe, num: 9 },
  ...>    %{ name: Cami, num: 3 },
  ...>    %{ name: Cassidy, num: 4 }
  ...>  ]
  iex> RWC_303.num_pie(arr, 8)
  2 # 16 pieces needed, pies can be cut into 8 pieces, so 2 pies should be
  bought
  """

  def num_pie(input, count) do
    input
    |> Enum.reduce(0, &(&2 + &1[:num]))
    |> div(count)
  end
end

p304.ex

defmodule RWC_304 do
  @doc """
  Given an array arr and integers n and m, remove n elements from the front of
  the array, and m elements from the back. Assume that n + m <= arr.length.

  Example:

  iex> RWC_304.trim_array([1, 2, 3, 4, 5, 6], 2, 1)
  [3, 4, 5]

  iex> RWC_304.trim_array([6, 2, 4, 3, 7, 1, 3], 5, 0)
  [1, 3]

  iex> RWC_304.trim_array([1, 7], 0, 0)
  [1, 7]
  """

  def trim_array(input, n, m) do
    input
    |> Enum.slice(n, length(input) - n - m)
  end
end

p305.ex

defmodule RWC_305 do
  @doc """
  Given some JSON data, calculate the maximum depth reached. Both arrays and
  dictionaries increase the depth! If the input is invalid data, the response
  should be undefined (you decide how you want that to return).

  iex> RWC_305.depth_json([])
  1

  iex> RWC_305.depth_json([1, 2, 3, 4, 5])
  1

  iex> RWC_305.depth_json([%{a: []}, ["abc"]])
  3
  """
  def depth_json(input), do: compute_depth(input)

  defp compute_depth(input) when is_list(input) or is_map(input) do
    cond do
      is_list(input) and input == [] ->
        1

      true ->
        input
        |> flatten_if_map()
        |> Enum.map(&compute_depth/1)
        |> Enum.max()
        |> Kernel.+(1)
    end
  end

  defp compute_depth(_), do: 0

  defp flatten_if_map(input) when is_map(input), do: Map.values(input)
  defp flatten_if_map(input), do: input
end

p306.ex

defmodule RWC_306 do
  @doc """
  Write a function that takes an array of consecutive, increasing letters as
  input, and returns any missing letters in the array between the first and last
  letter.

  Example:

  iex> RWC_306.missing_letters(["a","b","c","d","f"])
  ["e"]


  iex> RWC_306.missing_letters([
  ...>   "a", "b", "c", "d", "e", "h", "i", "j", "k", "l", "m", "n", "o",
  ...>   "p", "q", "r", "s", "t", "u", "w", "x", "y", "z"
  ...> ])
  ["f", "g", "v"]
  """

  def missing_letters(input) do
    input_complete_mapset =
      input
      |> then(fn list ->
        [head | _] = list
        tail = List.last(list)

        hd(to_charlist(head))..hd(to_charlist(tail))
        |> MapSet.new()
      end)

    input_mapset =
      input
      |> MapSet.new(&hd(to_charlist(&1)))

    input_complete_mapset
    |> MapSet.difference(input_mapset)
    |> MapSet.to_list()
    |> List.to_string()
    |> String.graphemes()
  end
end

p307.ex

defmodule RWC_307 do
  @doc """
  Given an integer n, return true if it's a perfect square AND when reversed, is
  still a perfect square.


  iex> RWC_307.reversed_squares(9)
  true

  iex> RWC_307.reversed_squares(441)
  true

  iex> RWC_307.reversed_squares(25)
  false
  """

  def reversed_squares(input) do
    input
    |> Integer.digits()
    |> Enum.reverse()
    |> Integer.undigits()
    |> then(
      &cond do
        is_perfect_square(&1) and is_perfect_square(input) -> true
        true -> false
      end
    )
  end

  defp is_perfect_square(input) do
    input
    |> :math.sqrt()
    |> then(&if Kernel.trunc(&1) == &1, do: true, else: false)
  end
end

p308.ex

defmodule RWC_308 do
  @doc """
  Given an array of strings and a max width, format the text such that each line
  has exactly maxWidth characters and is fully justified. You can choose how you
  want to wrap a word.

  Example:

  iex> RWC_308.justify_text(
  ...>   ["This", "is", "an", "example", "of", "text", "justification."],
  ...>   16
  ...> )
  [
    "This    is    an", "example  of text", "justification.  "
  ]
  """

  def justify_text(input, max_length) do
    input
    |> Enum.reduce([[]], fn word, phrase_list ->
      phrase_list
      |> List.last([])
      |> then(fn last_phrase ->
        current_phrase_length = last_phrase |> Enum.join(".") |> String.length()

        cond do
          current_phrase_length + String.length(word) < max_length ->
            # update last element
            last_list =
              phrase_list
              |> Enum.at(-1)
              |> Enum.concat([word])

            phrase_list
            |> Enum.drop(-1)
            |> Enum.concat([last_list])

          true ->
            # move to new phrase
            phrase_list
            |> Enum.concat([[word]])
        end
      end)
    end)
    |> Enum.map(&justify_phrase(&1, max_length))
  end

  defp justify_phrase(input, max_length) do
    number_of_spaces_to_add =
      max_length - (input |> Enum.join("") |> String.length())

    number_of_breaks = if length(input) == 1, do: 1, else: length(input) - 1
    each_space_block_length = div(number_of_spaces_to_add, number_of_breaks)
    remainder = rem(number_of_spaces_to_add, number_of_breaks)

    spaces_list =
      " "
      |> list_from(each_space_block_length)
      |> list_from(number_of_breaks)
      |> then(fn [first_break_spaces | rest] ->
        case remainder do
          0 ->
            [first_break_spaces | rest]

          _ ->
            first_break_spaces
            |> Enum.concat(list_from(" ", remainder))
            |> then(&[&1 | rest])
        end
      end)
      |> then(
        &cond do
          length(input) == 1 -> &1
          true -> Enum.concat(&1, [[""]])
        end
      )

    input
    |> Enum.zip(spaces_list)
    |> Enum.reduce("", fn {word, spaces}, line ->
      "#{line}#{word}#{Enum.join(spaces)}"
    end)
  end

  defp list_from(el, count), do: for(_ <- 1..count, do: el)
end

p309.ex

defmodule RWC_309 do
  @doc """
  Given a string, separate it into groups of non-space equal characters, sorted.

  Example:

  iex> RWC_309.explode_string("Ahh, abracadabra!")
  ["!",",","A","aaaaa","bb","c","d","hh","rr"]
  """

  def explode_string(input) do
    input
    |> String.replace(" ", "")
    |> String.split("", trim: true)
    |> Enum.frequencies()
    |> Map.to_list()
    |> Enum.map(fn {char, count} ->
      list_from(char, count)
      |> Enum.join()
    end)
  end

  defp list_from(el, count), do: for(_ <- 1..count, do: el)
end

p310.ex

defmodule RWC_310 do
  @doc """
  Given an array where each element is the price of a given stock on that
  index's day, choose a single day to buy a stock and a different day (in the
  future/later in the array) to sell the stock to maximize your profit. Return
  the maximum profit that you can get from a given input. If you can't profit,
  return 0.

  Example:

  iex> RWC_310.maximum_profit([7, 1, 5, 3, 6, 4])
  5    # Buy on day 2, and sell on day 5, your profit = 6 - 1 = 5.
  """

  def maximum_profit(input) do
    input
    |> Enum.with_index()
    |> Enum.reduce(0, fn {price, index}, max_profit ->
      input
      |> Enum.slice((index + 1)..-1)
      |> Enum.max(&>=/2, fn -> 0 end)
      |> Kernel.-(price)
      |> then(
        &cond do
          &1 > max_profit -> &1
          true -> max_profit
        end
      )
    end)
  end
end

p311.ex

defmodule RWC_311 do
  @doc """
  Given two strings s and t, return true if t is an anagram of s, and false
  otherwise. Try this in a language you're not comfortable with!

  Example:

  iex> RWC_311.is_anagram("barbie", "oppenheimer")
  false

  iex> RWC_311.is_anagram("race", "care")
  true
  """

  def is_anagram(a, b), do: get_chars(a) === get_chars(b)

  defp get_chars(input),
    do: input |> String.split("", trim: true) |> Enum.frequencies()
end

p312.ex

defmodule RWC_312 do
  @doc """
  Implement the Luhn algorithm to validate a credit card number. Bonus points if
  you can identify what brand of credit card the user inputted!

  iex> RWC_312.luhn_check(123456789)
  false

  iex> RWC_312.luhn_check(5555555555554444)
  true
  """

  def luhn_check(input) do
    input
    |> Integer.digits()
    |> Enum.with_index(1)
    |> Enum.reduce(0, fn {digit, index}, sum ->
      cond do
        rem(index, 2) == 0 -> digit * 2
        true -> digit
      end
      |> Integer.digits()
      |> Enum.sum()
      |> Kernel.+(sum)
    end)
    |> then(&(rem(&1, 10) == 0))
  end
end

p313.ex

defmodule RWC_313 do
  @doc """
  You have a faulty keyboard. Whenever you type a vowel on it (a,e,i,o,u,y), it
  reverses the string that you have written, instead of typing the character.
  Typing other characters works as expected. Given a string, return what will be
  on the screen after typing with your faulty keyboard.

  Example:

  iex> RWC_313.faulty_keeb("string")
  "rtsng"

  iex> RWC_313.faulty_keeb("hello world!")
  "w hllrld!"
  """

  @vowels ["a", "e", "i", "o", "u", "y"]

  def faulty_keeb(input) do
    input
    |> String.graphemes()
    |> Enum.reduce([], fn char, word ->
      cond do
        Enum.member?(@vowels, char) -> Enum.reverse(word)
        true -> Enum.concat(word, [char])
      end
    end)
    |> Enum.join()
  end
end

p314.ex

defmodule RWC_314 do
  @doc """
  Make a "guessing game" where there is a target number, and as the user makes
  guesses, the output returns higher or lower until the user is correct.

  Example usage:

  Guess the number!
  > 10
  higher
  > 20
  higher
  > 30
  lower
  > 25
  higher
  > 27
  Correct! You won in 5 guesses!
  """

  def solve(guess) do
    IO.puts("Guess the number!")

    input()
    |> solve(guess)
  end

  def solve(guess, answer, guess_count \\ 1)

  def solve(guess, answer, 1) when guess === answer,
    do: IO.puts("Correct! You won in 1 guess!") |> exit()

  def solve(guess, answer, guess_count) when guess === answer,
    do: IO.puts("Correct! You won in #{guess_count} guesses!") |> exit()

  def solve(guess, answer, guess_count) do
    cond do
      guess > answer ->
        IO.puts("lower")

      guess < answer ->
        IO.puts("higher")
    end

    input()
    |> solve(answer, guess_count + 1)
  end

  defp input() do
    IO.gets("> ")
    |> Integer.parse()
    |> then(&elem(&1, 0))
  end
end

RWC_314.solve(:rand.uniform(100))

p315.ex

defmodule RWC_315 do
  @moduledoc """
  Given a sequence of numbers, generate a "count and say" string.

  Example:

  iex> RWC_315.count_and_say(112222555)
  "two 1s, then four 2s, then three 5s"

  iex> RWC_315.count_and_say(3333333333)
  "ten 3s"
  """

  @number_say_map %{
    1 => "one",
    2 => "two",
    3 => "three",
    4 => "four",
    5 => "five",
    6 => "six",
    7 => "seven",
    8 => "eight",
    9 => "nine",
    10 => "ten"
  }

  def count_and_say(input) do
    input
    |> Integer.digits()
    # count
    |> Enum.reduce([], fn number, list ->
      current_list = List.first(list, [nil])

      current_list
      |> List.first()
      |> then(fn current_digit ->
        case current_digit do
          # same digit as current
          ^number ->
            list
            |> List.delete_at(0)
            |> then(&[[number | current_list] | &1])

          # new digit
          _ ->
            [[number] | list]
        end
      end)
    end)
    |> Enum.reverse()
    # say
    |> Enum.map_join(", then ", fn list ->
      len = Map.get(@number_say_map, length(list))
      "#{len} #{List.first(list)}s"
    end)
  end
end

p316.ex

defmodule RWC_316 do
  @moduledoc """
  Given an array of integers and a number k (where k is guaranteed to be less
  than the array's length), return a subarray of length k with the minimum
  possible sum. Maintain the order of the original array!

  Example:

  iex> RWC_316.min_subs([1, 3, 20, 4, 8, 9, 11], 3)
  [4, 8, 9]

  iex> RWC_316.min_subs([4, 4, 4, 4, 8], 2)
  [4, 4]
  """

  def min_subs(input, len) do
    input
    |> Enum.chunk_every(len, 1, :discard)
    |> Enum.min_by(&Enum.sum/1)
  end
end

p317.ex

defmodule RWC_317 do
  @moduledoc """
  Given an array of integers, sort them into two separate sorted arrays of even
  and odd numbers. If you see a zero, skip it.

  Example:

  iex> RWC_317.separate_and_sort([4, 3, 2, 1, 5, 7, 8, 9])
  [[2, 4, 8], [1, 3, 5, 7, 9]]

  iex> RWC_317.separate_and_sort([1,1,1,1])
  [[], [1,1,1,1]]
  """

  def separate_and_sort(input) do
    input
    |> Enum.sort()
    |> Enum.split_with(&(rem(&1, 2) == 0))
    |> Tuple.to_list()
  end
end

p318.ex

defmodule RWC_318 do
  @moduledoc """
  You have n equal-sized blocks and you want to build a staircase with them.
  Return the number of steps you can fully build.

  iex> RWC_318.build_staircase(6)
  3

  #=> #
  #=> ##
  #=> ###

  iex> RWC_318.build_staircase(9)
  3 #=> it takes 10 blocks to make 4 steps
  """

  def build_staircase(input) do
    1..input
    |> Enum.reduce_while(0, fn step, total ->
      cond do
        total + step > input -> {:halt, step - 1}
        true -> {:cont, total + step}
      end
    end)
  end
end

p322.ex

defmodule RWC_322 do
  @moduledoc """
  Given two strings s and t, determine if they are isomorphic. Two strings are
  isomorphic if there is a one-to-one mapping possible for every character of
  the first string to every character of the second string.

  iex> RWC_322.is_isomorphic("abb", "cdd")
  true # "a" maps to "c" and "b" maps to "d"

  iex> RWC_322.is_isomorphic("cassidy", "1234567")
  false # "s" cannot have a mapping to both "3" and "4"

  iex> RWC_322.is_isomorphic("cass", "1233")
  true
  """

  def is_isomorphic(first, second) do
    [first, second]
    |> Enum.map(fn string ->
      string
      |> String.split("", trim: true)
      |> Enum.frequencies()
      |> Map.values()
    end)
    |> then(fn [f1, f2] -> f1 == f2 end)
  end
end

p323.ex

defmodule RWC_323 do
  @moduledoc """
  Given a string s, you are allowed to delete at most k characters. Find if the
  string can be a palindrome after deleting at most k characters.

  iex> RWC_323.k_pal("abcweca", 2)
  true

  iex> RWC_323.k_pal("abcweca", 1)
  false

  iex> RWC_323.k_pal("acwca", 2)
  true

  iex> RWC_323.k_pal("acxcb", 1)
  false
  """

  def k_pal(string, count) do
    string
    |> String.graphemes()
    |> check_first_and_last_characters(count)
  end

  defp check_first_and_last_characters([_char], _count), do: true
  defp check_first_and_last_characters([char | [char]], _count), do: true

  defp check_first_and_last_characters(string, count) do
    [first | with_last] = string
    [last | remaining_reversed] = Enum.reverse(with_last)
    remaining = Enum.reverse(remaining_reversed)

    cond do
      first == last ->
        check_first_and_last_characters(remaining, count)

      first != last and count == 0 ->
        false

      first != last and count > 0 ->
        check_first_and_last_characters([first | remaining], count - 1) or
          check_first_and_last_characters(with_last, count - 1)

      true ->
        false
    end
  end
end

p325.ex

defmodule RWC_325 do
  @moduledoc """
  Given a list of words and a dictionary of letter scores, find the word with
  the highest score according to the rules:

  score = word_length * (sum of letter scores in the word)

  If there are multiple words with the same highest score, return the
  lexicographically smallest one.

  iex> word_list = ["apple", "banana", "cherry", "date", "fig"];
  ...> RWC_325.score_word_game(word_list)
  "cherry"
  """

  def score_word_game(word_list, _letter_scores \\ nil) do
    word_list
    |> Enum.map(&get_word_score/1)
    |> Enum.max_by(fn {_word, score} -> score end)
    |> then(&elem(&1, 0))
  end

  defp get_word_score(word) do
    word
    |> String.downcase()
    |> String.graphemes()
    |> Enum.reduce(0, fn letter, total ->
      score = (to_charlist(letter) |> hd()) - 96

      total + score
    end)
    |> then(&{word, &1})
  end
end

p326.ex

defmodule RWC_326 do
  @moduledoc """
  Given a list of tasks, where each task has a duration, and a limited amount of
  available time to work, write a function to return the tasks that can be
  completed within the given time, without re-ordering the original list of
  tasks. Try to maximize the number of tasks that can be completed!

  Example:

  iex> tasks = [
  ...>    %{ name: "Task 1", duration: 4 },
  ...>    %{ name: "Task 2", duration: 2 },
  ...>    %{ name: "Task 3", duration: 7 },
  ...>    %{ name: "Task 4", duration: 5 },
  ...>    %{ name: "Task 5", duration: 1 },
  ...>    %{ name: "Task 6", duration: 3 }
  ...>  ];
  ...> time_to_work = 6;
  ...> RWC_326.do_tasks(tasks, time_to_work)
  ["Task 2", "Task 5", "Task 6"]
  """

  def do_tasks(task_list, time_to_work) do
    task_list
    |> Enum.with_index()
    |> Enum.sort_by(fn {%{duration: duration}, _index} -> duration end)
    |> Enum.reduce_while({0, []}, fn {%{duration: duration}, index},
                                     {time_sum, indices} ->
      cond do
        time_sum + duration > time_to_work -> {:halt, indices}
        true -> {:cont, {time_sum + duration, [index | indices]}}
      end
    end)
    |> Enum.sort()
    |> Enum.map(
      &(task_list
        |> Enum.at(&1)
        |> then(fn %{name: name} -> name end))
    )
  end
end

p327.ex

defmodule RWC_327 do
  @moduledoc """
  Given a start number a, an ending number b, and a string str that can be
  "odd", "even", or "prime", return all of the numbers that are odd, even, or
  prime between a and b. a will not always necessarily be less than b!


  iex> RWC_327.between_nums(3, 11, "even")
  [4,6,8,10]

  iex> RWC_327.between_nums(15, 1, "prime")
  [2,3,5,7,11,13]
  """

  defp is_prime(num) do
    cond do
      num <= 1 ->
        false

      num == 2 ->
        true

      rem(num, 2) == 0 ->
        false

      true ->
        3..(num - 1)//2
        |> Enum.all?(&(rem(num, &1) != 0))
    end
  end

  def between_nums(start, finish, option) when start > finish,
    do: between_nums(finish, start, option)

  def between_nums(start, finish, option) do
    start..finish
    |> Enum.filter(fn num ->
      case option do
        "prime" ->
          is_prime(num)

        "even" ->
          rem(num, 2) == 0

        _ ->
          rem(num, 2) != 0
      end
    end)
  end
end

p328.ex

defmodule RWC_328 do
  @moduledoc """
  Given two arrays calories and prices, where calories[i] and prices[i]
  represent the calorie content and price of the ith food item, and a daily
  calorie goal, find the minimum cost to achieve or exceed the daily calorie
  goal. If it's impossible to meet the goal, return -1.

  Example:

  iex> calories = [200, 400, 600, 800]
  ...> prices = [50, 60, 80, 100]
  ...> daily_goal = 1200
  ...> RWC_328.min_cost_for_calories(calories, prices, daily_goal)

  160 # the 2nd and 4th items add up to 1200 calories for the minimum cost
  """

  def min_cost_for_calories(calories, prices, daily_goal) do
    calories
    |> Enum.with_index()
    |> Enum.flat_map(fn {calorie, index} ->
      calories
      |> Enum.with_index()
      |> Enum.slice(index..-1)
      |> Enum.filter(&(elem(&1, 0) != calorie))
      |> Enum.map(&{elem(&1, 0) + calorie, {index, elem(&1, 1)}})
    end)
    |> Enum.filter(&(elem(&1, 0) >= daily_goal))
    |> Enum.reduce(:infinity, fn {_calories, {index_a, index_b}}, total_price ->
      current_combo_price = Enum.at(prices, index_a) + Enum.at(prices, index_b)

      cond do
        current_combo_price < total_price -> current_combo_price
        true -> total_price
      end
    end)
  end
end

p329.ex

defmodule RWC_329 do
  @moduledoc """
  There is a sorted integer array that has been rotated an unknown number of
  times. Given that rotated array, return how many times it has been rotated. It
  may contain duplicate numbers!

  iex> RWC_329.rotated_num([4, 0, 1, 2, 3])
  1

  iex> RWC_329.rotated_num([7, 9, 20])
  0

  iex> RWC_329.rotated_num([7, 7, 314, 1337, 7])
  4
  """

  def rotated_num(nums) do
    cond do
      Enum.sort(nums) == nums -> 0
      true -> 1 + rotated_num(Enum.slide(nums, 0, -1))
    end
  end
end

p330.ex

defmodule RWC_330 do
  @moduledoc """
  Given an array of integers, return the majority element. If there is no
  majority element, return if the array is majority even or odd numbers, and if
  there is none, say so.

  iex> RWC_330.majority([3,1,4,1])
  "1"

  iex> RWC_330.majority([33,44,55,66,77])
  "Majority odds"

  iex> RWC_330.majority([1,2,3,4])
  "No majority"
  """

  def majority(nums) do
    nums
    |> Enum.frequencies()
    |> Map.to_list()
    |> Enum.sort_by(fn {_, count} -> count end, :desc)
    |> then(fn [{possible_majority, first} | [{_, second} | _]] ->
      cond do
        first == second ->
          nums
          |> Enum.group_by(&(rem(&1, 2) == 0))
          |> then(fn %{false: odds, true: evens} ->
            cond do
              length(odds) > length(evens) -> "Majority odds"
              length(odds) > length(evens) -> "Majority evens"
              true -> "No majority"
            end
          end)

        true ->
          Integer.to_string(possible_majority)
      end
    end)
  end
end

p331.ex

defmodule RWC_331 do
  @moduledoc """
  Write a function that determines if an array of numbers is a bitonic sequence.
  A bitonic sequence is a sequence of numbers in which the numbers are in
  increasing order, and after a certain point, they start decreasing. Extra
  credit: print the peak number in the sequence!

  iex> RWC_331.is_bitonic([1,2,3,2])
  3 # true, extra credit: 3

  iex> RWC_331.is_bitonic([1,2,3])
  false

  iex> RWC_331.is_bitonic([3,4,5,5,5,2,1])
  5 # true, extra credit: 5
  """

  def is_bitonic(list) do
    list
    |> Enum.reduce_while({Enum.at(list, 0), :asc}, fn num, {peak, trend} ->
      cond do
        num >= peak and trend == :asc -> {:cont, {num, :asc}}
        num < peak and trend == :asc -> {:cont, {peak, :desc}}
        num < peak and trend == :desc -> {:cont, {peak, :desc}}
        true -> {:halt, {peak, :err}}
      end
    end)
    |> then(fn
      {_, :err} -> false
      {_, :asc} -> false
      {peak, :desc} -> peak
    end)
  end
end

p332.ex

defmodule RWC_332 do
  @moduledoc """
  You have some gifts you want to return. Gifts bought in December have a 90-day
  return window, and all other gifts have a 30-day return window. Given a gift's
  buy date, write a function that prints the last day you can return the gift.
  You can choose how dates should be formatted!

  # Given date: "Dec 25, 2023"

  iex> RWC_332.return_gift("2023-12-25")
  "2024-03-23" # 90 days

  iex> RWC_332.return_gift("2023-11-25")
  "2023-12-24" # 30 days
  """

  def return_gift(date) do
    date
    |> String.split("-")
    |> case do
      # December
      [_, "12", _] -> 90 - 1
      _ -> 30 - 1
    end
    |> then(fn days ->
      date
      |> Date.from_iso8601!()
      |> Date.add(days)
      |> Date.to_iso8601()
    end)
  end
end

p333.ex

defmodule RWC_333 do
  @moduledoc """
  Write a program that prints Happy new year! without using the string/character
  literals for the characters in the string!

  iex> RWC_333.wish_happy_new_year()
  "Happy New Year"
  """

  def wish_happy_new_year() do
    # Charlist
    [72, 97, 112, 112, 121, 32, 78, 101, 119, 32, 89, 101, 97, 114]
    |> to_string()
  end
end

p334.ex

defmodule RWC_334 do
  @moduledoc """
  You have an array of letters. Return the number of possible sequences of
  letters you can make using the letters in the array. Extra credit: print the
  sequences!

  iex> RWC_334.letters(["X"])
  1

  iex> RWC_334.letters(["A", "A", "B"])
  8 # "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA"
  """

  def permutations([]), do: [[]]

  def permutations(char_list),
    do:
      for(
        char <- char_list,
        rest <- permutations(char_list -- [char]),
        do: [char | rest]
      )

  def letters(char_list) do
    1..length(char_list)
    |> Enum.flat_map(fn chunk_len ->
      char_list
      |> Enum.chunk_every(chunk_len, 1)
      |> Enum.flat_map(fn chunk ->
        chunk
        |> permutations()
        |> Enum.map(&Enum.join/1)
      end)
    end)
    |> Enum.uniq()
    |> Enum.count()
  end
end

p335.ex

defmodule RWC_335 do
  @moduledoc """
  Given a 2D array, write a function that flips it vertically or horizontally.

  iex> array = [
  ...>   [1,2,3],
  ...>   [4,5,6],
  ...>   [7,8,9]
  ...> ]
  iex> RWC_335.flip(array, "horizontal")
  [[3,2,1],[6,5,4],[9,8,7]]
  iex> RWC_335.flip(array, "vertical")
  [[7,8,9],[4,5,6],[1,2,3]]
  """

  def flip(lists, "horizontal"),
    do:
      lists
      |> Enum.zip_with(&Function.identity/1)
      |> Enum.zip_with(&Enum.reverse/1)

  def flip(lists, "vertical"),
    do:
      lists
      |> Enum.zip_with(&Enum.reverse/1)
      |> Enum.zip_with(&Function.identity/1)
end

p360.ex

defmodule RWC_360 do
  @moduledoc """
  Write a function that takes an array of integers representing the number of
  flowers planted in a line, and an integer k representing the number of
  additional flowers you want to plant. Return whether it's possible to plant
  all k flowers without planting any two flowers adjacent to each other.


  iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1], 1)
  true # you can plant 1 flower between the others

  iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1], 2)
  false

  iex> RWC_360.can_plant_flowers([0, 0, 0, 0, 0], 3)
  true

  iex> RWC_360.can_plant_flowers([1, 0, 1, 0, 1], 1)
  false

  iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1, 0, 1], 1)
  true

  iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 0, 1, 0, 1], 2)
  false

  iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 0, 0, 1, 0, 1], 2)
  true
  """

  def can_plant_flowers(flowers, count) do
    flowers
    |> then(fn flowers ->
      flowers
      |> pad_ones()
      |> Enum.reverse()
      |> pad_ones()
      |> Enum.reverse()
    end)
    |> Enum.chunk_by(&(&1 == 1))
    |> Enum.filter(&Enum.all?(&1, fn x -> x == 0 end))
    |> Enum.map(fn zeros_list ->
      zeros_list
      |> Enum.chunk_every(3, 2, :discard)
      |> Enum.count(&(&1 == [0, 0, 0]))
      |> then(&(&1 >= count))
    end)
    |> Enum.any?(& &1)
  end

  defp pad_ones(flowers) do
    flowers
    |> Enum.take(2)
    |> case do
      [0, 0] ->
        [0 | flowers]

      _ ->
        flowers
    end
  end
end

p361.ex

defmodule RWC_361 do
  @moduledoc """
  Given an integer array nums, return the length of the longest increasing
  subsequence.

  iex> RWC_361.increasing_subsequence([10, 9, 2, 3, 7, 101, 18])
  4

  iex> RWC_361.increasing_subsequence([4, 4, 4, 4, 3])
  1
  """

  def increasing_subsequence(input) do
    input
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.map(fn [a, b] -> a < b end)
    |> Enum.chunk_by(& &1)
    |> Enum.flat_map(fn
      [true | _] = sub -> [length(sub)]
      _ -> []
    end)
    |> Enum.max(&>=/2, fn -> 0 end)
    |> then(&(&1 + 1))
  end
end

p364.ex

defmodule RWC_364 do
  @moduledoc """
  Create a function that should take one argument n, which is a positive
  integer. The function should return the sum of all squared positive integers
  between 1 and n, inclusive.


  iex> RWC_364.squares(5)
  55

  iex> RWC_364.squares(10)
  385

  iex> RWC_364.squares(25)
  5525

  iex> RWC_364.squares(100)
  338350
  """

  def squares(num, sum \\ 0)

  def squares(0, sum), do: sum

  def squares(num, sum), do: squares(num - 1, sum + num * num)
end

p386.ex

defmodule RWC_386 do
  @moduledoc """
  Write a function that generates all possible permutations of a given string.

  iex> RWC_386.permute("abc")
  ["abc", "acb", "bac", "bca", "cab", "cba"]
  """

  def get_permutations([]), do: [[]]

  def get_permutations(list),
    do: for(el <- list, rest <- get_permutations(list -- [el]), do: [el | rest])

  def permute(input) do
    input
    |> String.graphemes()
    |> get_permutations()
    |> Enum.map(&Enum.join/1)
  end
end

p389.ex

defmodule RWC_389 do
  @moduledoc """
  Given two strings, s and p, return an array of all the start indices of p's
  anagrams in s.

  iex> RWC_389.find_anagrams("cbaebabacd", "abc")
  [0, 6]

  iex> RWC_389.find_anagrams("fish", "cake")
  []

  iex> RWC_389.find_anagrams("abab", "ab")
  [0, 1, 2]
  """

  def find_anagrams(s, p) do
    p_sorted = p |> String.graphemes() |> Enum.sort()

    s
    |> String.graphemes()
    |> Enum.chunk_every(String.length(p), 1, :discard)
    |> Enum.map(&Enum.sort/1)
    |> Enum.with_index()
    |> Enum.flat_map(fn
      {^p_sorted, i} -> [i]
      _ -> []
    end)
  end
end

p390.ex

defmodule RWC_390 do
  @moduledoc """
  Write a function that evaluates a postfix expression (also known as Reverse
  Polish Notation) and returns the result. The expression will contain
  single-digit integers and the operators +, -, *, and /. You can assume the
  input is always a valid expression!

  iex> RWC_390.evaluate_postfix("12+")
  3

  iex> RWC_390.evaluate_postfix("56+7*")
  77
  """

  @op %{
    "+" => &Kernel.+/2,
    "-" => &Kernel.-/2,
    "*" => &Kernel.*/2,
    "/" => &div/2
  }

  def evaluate_postfix(input) do
    input
    |> String.graphemes()
    |> Enum.reduce({}, fn
      el, {} ->
        {String.to_integer(el)}

      el, {num} when el not in ["+", "-", "/", "*"] ->
        {num, String.to_integer(el)}

      el, {first, second} ->
        {@op[el].(first, second)}
    end)
    |> elem(0)
  end
end

p394.ex

defmodule RWC_394 do
  @moduledoc """
  A store is going out of business and will reduce the price of all products by
  10% every week leading up to the closing date. Given the closingDate,
  visitDate, and the originalPrice of a product, write a function that returns
  the price of the product on the visitDate. You can assume that originalPrice
  is a positive number.

  iex> RWC_394.calculate_price("2025-04-01", "2025-03-03", 100)
  65.61

  iex> RWC_394.calculate_price("2025-04-01", "2025-03-15", 50)
  40.5

  iex> RWC_394.calculate_price("2025-04-01", "2025-04-15", 75)
  75
  """

  def calculate_price(closing, visit, orig) do
    Date.diff(Date.from_iso8601!(closing), Date.from_iso8601!(visit))
    |> div(7)
    |> then(fn
      weeks when weeks < 0 ->
        orig

      weeks ->
        1..weeks
        |> Enum.reduce(orig, fn _, price ->
          price * 0.9
        end)
        |> Float.round(2)
    end)
  end
end

p397.ex

defmodule RWC_397 do
  @moduledoc """
  Write a function that finds the longest streak of consecutive true values in a
  boolean array that meets or exceeds a given streak goal. Return 0 if no such
  streak exists.

  iex> RWC_397.find_longest_streak([true, true, false, true, true, true], 3)
  3

  iex> RWC_397.find_longest_streak([true, true, true, false, true], 4)
  0

  iex> RWC_397.find_longest_streak([true, true, true, true], 2)
  4
  """

  def find_longest_streak(streak, len) do
    streak
    |> Enum.chunk_by(& &1)
    |> Enum.filter(&Enum.all?/1)
    |> Enum.max_by(&length/1)
    |> length()
    |> then(fn
      x when x < len -> 0
      x -> x
    end)
  end
end

p420.ex

defmodule RWC_420 do
  @moduledoc """
  Imagine a simplified version of the game Battleship played on a 2D grid. The
  grid represents the sea, and each cell can either be empty (.) or contain a
  part of a ship (X). Ships are placed horizontally or vertically, and there are
  no adjacent ships. Given a grid, count the number of battleships in it.

  iex> ships = [
  ...>   ["X", "X", ".", "X"],
  ...>   [".", ".", ".", "X"],
  ...>   [".", ".", ".", "X"],
  ...>   [".", ".", ".", "."],
  ...> ]
  ...> RWC_420.number_of_ships(ships)
  2
  """

  def number_of_ships(ships) do
    ships
    # => rotate matrix
    |> Enum.zip_with(&Function.identity/1)
    |> then(&[ships, &1])
    |> Enum.map(&check/1)
    |> Enum.sum()
  end

  defp check(row) do
    ~r/[X]{2,}/
    |> Regex.scan(Enum.join(row))
    |> Enum.count()
  end
end

p421.ex

defmodule RWC_421 do
  @moduledoc """
  For an array of numbers, generate an array where for every element, all
  neighboring elements are added to itself, and return the sum of that array.

  iex> RWC_421.with_neighbours([])
  0

  iex> RWC_421.with_neighbours([1])
  1

  iex> RWC_421.with_neighbours([1, 4])
  10

  iex> RWC_421.with_neighbours([1, 4, 7])
  28

  iex> RWC_421.with_neighbours([1, 4, 7, 10])
  55

  iex> RWC_421.with_neighbours([-1, -2, -3])
  -14

  iex> RWC_421.with_neighbours([0.1, 0.2, 0.3])
  1.4

  iex> RWC_421.with_neighbours([1,-20,300,-4000,50000,-600000,7000000])
  12338842
  """

  def with_neighbours(nums) do
    [0, nums, 0]
    |> List.flatten()
    |> Enum.chunk_every(3, 1, :discard)
    |> Enum.map(&Enum.sum/1)
    |> Enum.sum()
  end
end

p422.ex

defmodule RWC_422 do
  @moduledoc """
  You are given an array of arrays, where each inner array represents the runs
  scored by each team in an inning of a baseball game: [[home1, away1], [home2,
  away2], ...]. Write a function that returns an object with the total runs for
  each team, which innings each team led, and who won the game.

  iex> RWC_422.analyze_baseball_game([[1, 0], [2, 2], [0, 3], [4, 1]])
  %{
    home_total: 7, away_total: 6, home_led_innings: [1, 2, 4], away_led_innings:
    [3], winner: "home"
  }
  """

  def analyze_baseball_game(innings) do
    analyze_innings(%{}, innings)
  end

  defp analyze_innings(score, []) do
    winner = if score.home_total > score.away_total, do: "home", else: "away"

    Map.put(score, :winner, winner)
  end

  defp analyze_innings(score, [[home, away] | rest]) do
    cond do
      home >= away ->
        Map.update(score, :home_led_innings, [home], &(&1 ++ [home]))

      true ->
        Map.update(score, :away_led_innings, [away], &(&1 ++ [away]))
    end
    |> Map.update(:home_total, home, &(&1 + home))
    |> Map.update(:away_total, away, &(&1 + away))
    |> analyze_innings(rest)
  end
end

p423.ex

defmodule RWC_423 do
  @moduledoc """
  Write a function that determines if a number is abundant, deficient, perfect,
  or amicable.

  iex> RWC_423.what_kind_of_number(6)
  "perfect"

  iex> RWC_423.what_kind_of_number(12)
  "abundant"

  iex> RWC_423.what_kind_of_number(4)
  "deficient"

  iex> RWC_423.what_kind_of_number(220)
  "amicable"
  """

  def what_kind_of_number(num) do
    sum = divisor_sum(num)

    cond do
      sum == num -> "perfect"
      sum != num && divisor_sum(sum) == num -> "amicable"
      sum > num -> "abundant"
      true -> "deficient"
    end
  end

  defp divisor_sum(1), do: 0

  defp divisor_sum(num) do
    1..(num - 1)
    |> Enum.filter(&(rem(num, &1) == 0))
    |> Enum.sum()
  end
end

p424.ex

defmodule RWC_424 do
  @moduledoc """
  Given the non-negative integer n, output the value of its hyperfactorial.

  iex> RWC_424.hyperfactorial(0)
  1

  iex> RWC_424.hyperfactorial(2)
  4

  iex> RWC_424.hyperfactorial(3)
  108

  iex> RWC_424.hyperfactorial(7)
  3319766398771200000
  """

  def hyperfactorial(0), do: 1

  def hyperfactorial(num) do
    1..num
    |> Enum.map(&Integer.pow(&1, &1))
    |> Enum.product()
  end
end

p425.ex

defmodule RWC_425 do
  @moduledoc """
  You're building a tool that tracks component edits and groups them into a
  changelog. Given an array of edit actions, each with a timestamp and a
  component name, return an array of grouped changelog entries. Edits to the
  same component within a 10-minute window should be merged into one changelog
  entry, showing the component name and the range of timestamps affected.

  iex> edits = [
  ...>   %{timestamp: "2025-10-06T08:00:00Z", component: "Header"},
  ...>   %{timestamp: "2025-10-06T08:05:00Z", component: "Header"},
  ...>   %{timestamp: "2025-10-06T08:20:00Z", component: "Header"},
  ...>   %{timestamp: "2025-10-06T08:07:00Z", component: "Footer"},
  ...>   %{timestamp: "2025-10-06T08:15:00Z", component: "Footer"}
  ...> ]
  ...> RWC_425.group_changelog_edits(edits)
  [
    %{component: "Footer", start: "2025-10-06T08:07:00Z", end:
    "2025-10-06T08:15:00Z"}, %{component: "Header", start:
    "2025-10-06T08:00:00Z", end: "2025-10-06T08:05:00Z"}, %{component: "Header",
    start: "2025-10-06T08:20:00Z", end: "2025-10-06T08:20:00Z"}
  ]
  """

  def group_changelog_edits(edits) do
    edits
    |> Enum.group_by(& &1.component)
    |> Enum.sort_by(fn {component, _} -> component end)
    |> Enum.flat_map(fn {component, edits} ->
      edits
      |> Enum.sort_by(& &1.timestamp)
      |> Enum.map(& &1.timestamp)
      |> Enum.reduce([], &merge_edit/2)
      |> Enum.reverse()
      |> Enum.map(fn {start, finish} ->
        %{component: component, start: start, end: finish}
      end)
    end)
  end

  defp merge_edit(timestamp, []), do: [{timestamp, timestamp}]

  defp merge_edit(timestamp, [{start, finish} | rest]) do
    if minutes_between(finish, timestamp) <= 10 do
      [{start, timestamp} | rest]
    else
      [{timestamp, timestamp}, {start, finish} | rest]
    end
  end

  defp minutes_between(start, finish) do
    {:ok, start, _} = DateTime.from_iso8601(start)
    {:ok, finish, _} = DateTime.from_iso8601(finish)

    DateTime.diff(finish, start, :minute)
  end
end

p426.ex

defmodule RWC_426 do
  @moduledoc """
  Given a CSV string where each row contains a name, age, and city (and values
  may be quoted, have embedded commas or escaped quotes), write a function that
  parses the CSV and outputs a formatted list of strings in the form: "Name, age
  Age, from City". Handle quoted fields containing commas and escaped quotes.

  iex> csv = [
  ...>   "name,age,city",
  ...>   ~s("Ryu, Mi-yeong",30,"Seoul"),
  ...>   ~s(Zoey,24,"Burbank")
  ...> ] |> Enum.join(<<10>>)
  ...> RWC_426.csv_to_list(csv) |> String.split(<<10>>)
  ["- Ryu, Mi-yeong, age 30, from Seoul", "- Zoey, age 24, from Burbank"]
  """

  def csv_to_list(csv) do
    csv
    |> String.split("\n", trim: true)
    |> tl()
    |> Enum.map(&format_row/1)
    |> Enum.join("\n")
  end

  defp format_row(row) do
    [name, age, city] = parse_row(row)

    "- #{name}, age #{age}, from #{city}"
  end

  defp parse_row(row), do: parse_row(String.graphemes(row), "", [], false)

  defp parse_row([], field, fields, _quoted), do: Enum.reverse([field | fields])

  defp parse_row(["\"", "\"" | rest], field, fields, true),
    do: parse_row(rest, field <> "\"", fields, true)

  defp parse_row(["\"" | rest], field, fields, quoted),
    do: parse_row(rest, field, fields, !quoted)

  defp parse_row(["," | rest], field, fields, false),
    do: parse_row(rest, "", [field | fields], false)

  defp parse_row([char | rest], field, fields, quoted),
    do: parse_row(rest, field <> char, fields, quoted)
end

p427.ex

defmodule RWC_427 do
  @moduledoc """
  Given a string str and an array of positive integers widths, write a function
  that splits the string into lines, each with the exact number of characters as
  specified by the corresponding width. Return an array of the substrings. Use
  the last width for any remaining characters if the array is shorter than
  needed.

  iex> RWC_427.split_by_widths("Supercalifragilisticexpialidocious", [5, 9, 4])
  ["Super", "califragi", "list", "icex", "pial", "idoc", "ious"]
  """

  def split_by_widths(str, widths) do
    split_by_widths(str, widths, List.last(widths), [])
  end

  defp split_by_widths("", _widths, _last, result), do: Enum.reverse(result)

  defp split_by_widths(str, [], last, result),
    do: split_by_widths(str, [last], last, result)

  defp split_by_widths(str, [width | rest], last, result) do
    <<chunk::binary-size(^width), rest_of_string::binary>> =
      String.pad_trailing(str, width)

    split_by_widths(String.trim_trailing(rest_of_string), rest, last, [
      String.trim_trailing(chunk) | result
    ])
  end
end

p428.ex

defmodule RWC_428 do
  @moduledoc """
  Given a field represented as an array of 0s and 1s, where 1 means that
  position needs protection, you can place a scarecrow at any index, and each
  scarecrow protects up to k consecutive positions centered around itself.
  Return the minimum set of indices where scarecrows should be placed so that
  all the positions with 1 are protected.

  iex> RWC_428.place_scarecrows([1, 1, 0, 1, 1, 0, 1], 3)
  [1, 4, 6]

  iex> RWC_428.place_scarecrows([1, 0, 1, 1, 0, 1], 3)
  [1, 4]

  iex> RWC_428.place_scarecrows([1, 1, 1, 1, 1], 1)
  [0, 1, 2, 3, 4]
  """

  def place_scarecrows(field, width) do
    protect(field, width, 0, [], -1)
  end

  defp protect(field, _width, index, scarecrows, _protected_until)
       when index >= length(field) do
    Enum.reverse(scarecrows)
  end

  defp protect(field, width, index, scarecrows, protected_until) do
    if Enum.at(field, index) == 1 && index > protected_until do
      radius = div(width, 2)
      scarecrow = min(index + radius, length(field) - 1)

      protect(
        field,
        width,
        scarecrow + radius + 1,
        [scarecrow | scarecrows],
        scarecrow + radius
      )
    else
      protect(field, width, index + 1, scarecrows, protected_until)
    end
  end
end

p429.ex

defmodule RWC_429 do
  @moduledoc """
  Given the current position of a knight as [row, col] in an 8x8 chess board
  represented as a 2D array, write a function to return all valid moves the
  knight can make.

  iex> RWC_429.knight_moves([4, 4])
  [[2, 3], [2, 5], [3, 2], [3, 6], [5, 2], [5, 6], [6, 3], [6, 5]]

  iex> RWC_429.knight_moves([0, 0])
  [[1, 2], [2, 1]]

  iex> RWC_429.knight_moves([1, 2])
  [[0, 0], [0, 4], [2, 0], [2, 4], [3, 1], [3, 3]]
  """

  def knight_moves([row, col]) do
    [[-2, -1], [-2, 1], [-1, -2], [-1, 2], [1, -2], [1, 2], [2, -1], [2, 1]]
    |> Enum.map(fn [row_offset, col_offset] ->
      [row + row_offset, col + col_offset]
    end)
    |> Enum.filter(fn [row, col] -> row in 0..7 && col in 0..7 end)
  end
end

p430.ex

defmodule RWC_430 do
  @moduledoc """
  You are given two sorted arrays, a and b, where a has a large enough size
  buffer at the end to hold b (which can be spaces, zeroes, or nulls). Write a
  function to merge b into a in sorted order.

  iex> RWC_430.merge([1, 3, 5, 0, 0, 0], [2, 4, 6])
  [1, 2, 3, 4, 5, 6]
  """

  def merge(a, b) do
    a
    |> Enum.take(length(a) - length(b))
    |> Kernel.++(b)
    |> Enum.sort()
  end
end

p431.ex

defmodule RWC_431 do
  @moduledoc """
  Given a positive integer n, write a function that returns an array containing
  all integers from 1 to n, where each integer i appears exactly i times in the
  result. For example, 3 should appear 3 times, 5 should appear 5 times, and so
  on. The order of the integers in the output array does not matter.

  iex> RWC_431.repeated_integers(4)
  [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]
  """

  def repeated_integers(count),
    do: Enum.flat_map(1..count, &List.duplicate(&1, &1))
end

p432.ex

defmodule RWC_432 do
  @moduledoc """
  Given an array of meal prep tasks for Thanksgiving, where each task is
  represented as [taskName, startTime, endTime], return the maximum number of
  non-overlapping tasks you can complete, along with the names of the chosen
  tasks in the order they were selected.

  iex> tasks = [
  ...>   ["Make Gravy", 10, 11],
  ...>   ["Mash Potatoes", 11, 12],
  ...>   ["Bake Rolls", 11, 13],
  ...>   ["Prep Salad", 12, 13]
  ...> ]
  ...> RWC_432.max_meal_prep_tasks(tasks)
  %{count: 3, chosen: ["Make Gravy", "Mash Potatoes", "Prep Salad"]}
  """

  def max_meal_prep_tasks(tasks) do
    chosen =
      tasks
      |> Enum.sort_by(fn [_task, _start, finish] -> finish end)
      |> Enum.reduce([], &choose_task/2)
      |> Enum.reverse()
      |> Enum.map(fn [task, _start, _finish] -> task end)

    %{count: length(chosen), chosen: chosen}
  end

  defp choose_task([_task, _start, _finish] = task, []), do: [task]

  defp choose_task(
         [_task, start, _finish] = task,
         [[_prev_task, _prev_start, previous_finish] | _rest] = chosen
       ) do
    if start >= previous_finish, do: [task | chosen], else: chosen
  end
end

p433.ex

defmodule RWC_433 do
  @moduledoc """
  There are 16 basic HTML Colors. Write a program to output them in ascending
  order by HEX value. Don't use any built-in sorting methods.

  iex> RWC_433.html_colors_by_hex()
  [
    "000000",
    "000080",
    "0000FF",
    "008000",
    "008080",
    "00FF00", "00FFFF",
    "800000",
    "800080",
    "808000",
    "808080",
    "C0C0C0", "FF0000", "FF00FF", "FFFF00", "FFFFFF"
  ]
  """

  def html_colors_by_hex do
    [
      "000000",
      "000080",
      "0000FF",
      "008000",
      "008080",
      "00FF00",
      "00FFFF",
      "800000",
      "800080",
      "808000",
      "808080",
      "C0C0C0",
      "FF0000",
      "FF00FF",
      "FFFF00",
      "FFFFFF"
    ]
  end
end

p434.ex

defmodule RWC_434 do
  @moduledoc """
  Make a data structure for a deck of cards, and implement a shuffle() method,
  and a draw(n) method. Calling draw() when the deck is empty returns an empty
  array.

  iex> deck = RWC_434.new()
  ...> {cards, deck} = RWC_434.draw(deck, 5)
  ...> {length(cards), length(deck)}
  {5, 47}

  iex> RWC_434.draw([], 5)
  []
  """

  def new do
    for suit <- ["♣", "♦", "♥", "♠"],
        rank <- [
          "A",
          "2",
          "3",
          "4",
          "5",
          "6",
          "7",
          "8",
          "9",
          "10",
          "J",
          "Q",
          "K"
        ] do
      rank <> suit
    end
  end

  def shuffle(deck), do: Enum.shuffle(deck)
  def draw([], _num), do: []

  def draw(deck, num) do
    Enum.split(deck, num)
  end
end

p435.ex

defmodule RWC_435 do
  @moduledoc """
  Write a function to generate a Latin Square given a positive integer n. The
  values can be any n distinct values, and don't have to be consistent for
  different n.

  iex> RWC_435.latin_square(1)
  [[1]]

  iex> RWC_435.latin_square(2)
  [[1, 2], [2, 1]]

  iex> RWC_435.latin_square(4)
  [
    [1, 2, 3, 4],
    [2, 3, 4, 1],
    [3, 4, 1, 2],
    [4, 1, 2, 3]
  ]
  """

  def latin_square(num) do
    0..(num - 1)
    |> Enum.map(fn row ->
      0..(num - 1)
      |> Enum.map(&(rem(row + &1, num) + 1))
    end)
  end
end

p436.ex

defmodule RWC_436 do
  @moduledoc """
  An alternating array is a list of any length in which two values are
  alternating (all even-indexed items are equal, and all odd-indexed items are
  equal). Given an array, return true if it is alternating.

  iex> RWC_436.alternating?([])
  true

  iex> RWC_436.alternating?([1])
  true

  iex> RWC_436.alternating?([1, 1])
  true

  iex> RWC_436.alternating?([1, 2, 1])
  true

  iex> RWC_436.alternating?([10, 5, 10, 5, 10])
  true

  iex> RWC_436.alternating?([2, 2, 3, 3])
  false

  iex> RWC_436.alternating?([5, 4, 3, 5, 4, 3])
  false
  """

  def alternating?(list) do
    list
    |> Enum.with_index()
    |> Enum.group_by(fn {_num, index} -> rem(index, 2) end, fn {num, _index} ->
      num
    end)
    |> Map.values()
    |> Enum.all?(fn nums -> Enum.uniq(nums) |> length() == 1 end)
  end
end

p437.ex

defmodule RWC_437 do
  @moduledoc """
  Given a string that contains only digits from 0 to 9 and a number n, replace
  each consecutive run of n with its length.

  iex> RWC_437.replace_repeats("1234500362000440", 0)
  "1234523623441"

  iex> RWC_437.replace_repeats("000000000000", 0)
  "12"

  iex> RWC_437.replace_repeats("123456789", 1)
  "123456789"
  """

  def replace_repeats(str, num) do
    digit = Integer.to_string(num)

    ~r/#{digit}+/
    |> Regex.replace(str, fn match ->
      Integer.to_string(String.length(match))
    end)
  end
end

p438.ex

defmodule RWC_438 do
  @moduledoc """
  Given an integer array nums, sum each element in the array in order. You are
  allowed to use at most one reset during the run: when you reset, your current
  score becomes 0 and you continue with the next elements. Return the maximum
  score you can end with.

  iex> RWC_438.max_score_with_one_reset([2, -1, 2, -5, 2, 2])
  4

  iex> RWC_438.max_score_with_one_reset([4, -10, 3, 2, -1, 6])
  10

  iex> RWC_438.max_score_with_one_reset([-50, -2, -3])
  0
  """

  def max_score_with_one_reset(nums) do
    nums
    |> Enum.reverse()
    |> Enum.scan(0, &(&1 + &2))
    |> then(&[0 | &1])
    |> Enum.max()
  end
end

p439.ex

defmodule RWC_439 do
  @moduledoc """
  Given an array of objects representing bears in a forest, each with a name and
  hunger level, return the names of all bears whose hunger level is above the
  forest average, sorted alphabetically.

  iex> bears = [
  ...>   %{name: "Baloo", hunger: 6},
  ...>   %{name: "Yogi", hunger: 9},
  ...>   %{name: "Paddington", hunger: 4},
  ...>   %{name: "Winnie", hunger: 10},
  ...>   %{name: "Chicago", hunger: 20}
  ...> ]
  ...> RWC_439.hungry_bears(bears)
  ["Chicago", "Winnie"]
  """

  def hungry_bears(bears) do
    average =
      bears
      |> Enum.map(& &1.hunger)
      |> then(&(Enum.sum(&1) / length(&1)))

    bears
    |> Enum.filter(&(&1.hunger > average))
    |> Enum.map(& &1.name)
    |> Enum.sort()
  end
end

p440.ex

defmodule RWC_440 do
  @moduledoc """
  Given a string `str`, find a contiguous substring of length `10` whose
  characters can be bijectively mapped to the moves `{U,D,L,R,B,A}` so that the
  substring decodes to the Konami code `"UUDDLRLRBA"`.

  iex> RWC_440.konami_mapping("xx2233454590yy11110")
  %{"0" => "A", "2" => "U", "3" => "D", "4" => "L", "5" => "R", "9" => "B"}

  iex> RWC_440.konami_mapping("sduwahoda22ii0d0dbn")
  %{"0" => "L", "2" => "U", "i" => "D", "d" => "R", "b" => "B", "n" => "A"}
  """

  @code String.graphemes("UUDDLRLRBA")

  def konami_mapping(str) do
    str
    |> String.graphemes()
    |> Enum.chunk_every(length(@code), 1, :discard)
    |> Enum.find_value(&mapping_for/1)
  end

  defp mapping_for(chars) do
    Enum.zip(chars, @code)
    |> Enum.reduce_while({%{}, %{}}, fn {char, move}, {mapping, reverse} ->
      cond do
        Map.get(mapping, char, move) != move ->
          {:halt, nil}

        Map.get(reverse, move, char) != char ->
          {:halt, nil}

        true ->
          {:cont, {Map.put(mapping, char, move), Map.put(reverse, move, char)}}
      end
    end)
    |> case do
      {mapping, _reverse} -> mapping
      nil -> nil
    end
  end
end

p441.ex

defmodule RWC_441 do
  @moduledoc """
  You are given a string consisting of lowercase words, each separated by a
  single space. Determine how many vowels appear in the first word. Then,
  reverse each following word that has the same vowel count.

  iex> RWC_441.flippedy("cat and mice")
  "cat dna mice"

  iex> RWC_441.flippedy("banana healthy")
  "banana healthy"
  """

  def flippedy(str) do
    [first | rest] = String.split(str)
    count = vowel_count(first)

    rest
    |> Enum.map(fn word ->
      if vowel_count(word) == count, do: String.reverse(word), else: word
    end)
    |> then(&Enum.join([first | &1], " "))
  end

  defp vowel_count(word),
    do: word |> String.graphemes() |> Enum.count(&(&1 in ~w(a e i o u)))
end

p442.ex

defmodule RWC_442 do
  @moduledoc """
  February 2026 is a perfect month! Write a function that returns the closest
  previous and next perfect month around the given Gregorian year.

  iex> RWC_442.nearest_perfect_months(2025)
  %{prev: "2021-02", next: "2026-02"}

  iex> RWC_442.nearest_perfect_months(2026)
  %{prev: "2026-02", next: "2027-02"}
  """

  def nearest_perfect_months(year) do
    %{prev: perfect_month_before(year), next: perfect_month_after(year + 1)}
  end

  defp perfect_month_before(year) do
    year
    |> Stream.iterate(&(&1 - 1))
    |> Enum.find(&perfect_february?/1)
    |> then(&"#{&1}-02")
  end

  defp perfect_month_after(year) do
    year
    |> Stream.iterate(&(&1 + 1))
    |> Enum.find(&perfect_february?/1)
    |> then(&"#{&1}-02")
  end

  defp perfect_february?(year) do
    not Calendar.ISO.leap_year?(year) and
      Date.day_of_week(Date.new!(year, 2, 1)) in [1, 7]
  end
end

p443.ex

defmodule RWC_443 do
  @moduledoc """
  Given an integer array and a number `n`, move all of the `n`s to the end of
  the array while maintaining the relative order of the non-`n`s.

  iex> RWC_443.move_nums([0, 2, 0, 3, 10], 0)
  [2, 3, 10, 0, 0]
  """

  def move_nums(nums, num) do
    Enum.reject(nums, &(&1 == num)) ++ Enum.filter(nums, &(&1 == num))
  end
end

p444.ex

defmodule RWC_444 do
  @moduledoc """
  You have a 2D grid of numbers. Write a function that zooms in by an integer
  factor `k >= 2` by turning each cell into a `k x k` block with the same value,
  returning the bigger grid.

  iex> RWC_444.zoom([[1, 2], [3, 4]], 2)
  [[1, 1, 2, 2], [1, 1, 2, 2], [3, 3, 4, 4], [3, 3, 4, 4]]

  iex> RWC_444.zoom([[7, 8, 9]], 3)
  [
    [7, 7, 7, 8, 8, 8, 9, 9, 9],
    [7, 7, 7, 8, 8, 8, 9, 9, 9],
    [7, 7, 7, 8, 8, 8, 9, 9, 9]
  ]

  iex> RWC_444.zoom([[1], [2]], 3)
  [
    [1, 1, 1],
    [1, 1, 1],
    [1, 1, 1],
    [2, 2, 2],
    [2, 2, 2],
    [2, 2, 2]
  ]
  """

  def zoom(grid, count) do
    grid
    |> Enum.flat_map(fn row ->
      row = Enum.flat_map(row, &List.duplicate(&1, count))
      List.duplicate(row, count)
    end)
  end
end

p445.ex

defmodule RWC_445 do
  @moduledoc """
  Given an array of integers, find the contiguous subarray that has the largest
  sum and return that sum.

  iex> RWC_445.max_subarray_sum([-2, 1, -3, 4, -1, 2, 1, -5, 4])
  6

  iex> RWC_445.max_subarray_sum([5])
  5

  iex> RWC_445.max_subarray_sum([-1, -2, -3, -4])
  -1

  iex> RWC_445.max_subarray_sum([5, 4, -1, 7, 8])
  23
  """

  def max_subarray_sum([first | rest]) do
    rest
    |> Enum.reduce({first, first}, fn num, {best, current} ->
      current = max(num, current + num)
      {max(best, current), current}
    end)
    |> elem(0)
  end
end

p446.ex

defmodule RWC_446 do
  @moduledoc """
  Find the majority element in an array (one that appears more than n/2 times)
  in `O(n)` time and `O(1)` space without hashmaps.

  iex> RWC_446.majority_element([2, 2, 1, 1, 2, 2, 1, 2, 2])
  2

  iex> RWC_446.majority_element([3, 3, 4, 2, 3, 3, 1])
  3
  """

  def majority_element(nums) do
    nums
    |> Enum.reduce({nil, 0}, fn
      num, {_, 0} -> {num, 1}
      num, {num, count} -> {num, count + 1}
      _num, {candidate, count} -> {candidate, count - 1}
    end)
    |> elem(0)
  end
end

p447.ex

defmodule RWC_447 do
  @moduledoc """
  Given a string `s` consisting only of `a` and `b`, return the minimum number
  of adjacent swaps needed to transform it into an alternating string, or `-1`
  if impossible.

  iex> RWC_447.min_swaps_to_alternate("aabb")
  1

  iex> RWC_447.min_swaps_to_alternate("aaab")
  -1

  iex> RWC_447.min_swaps_to_alternate("aaaabbbb")
  6
  """

  def min_swaps_to_alternate(str) do
    chars = String.graphemes(str)
    a_count = Enum.count(chars, &(&1 == "a"))
    b_count = length(chars) - a_count

    cond do
      abs(a_count - b_count) > 1 ->
        -1

      a_count > b_count ->
        swaps_to(chars, "a")

      b_count > a_count ->
        swaps_to(chars, "b")

      true ->
        min(swaps_to(chars, "a"), swaps_to(chars, "b"))
    end
  end

  defp swaps_to(chars, first) do
    chars
    |> Enum.with_index()
    |> Enum.filter(fn {char, _index} -> char == first end)
    |> Enum.map(&elem(&1, 1))
    |> Enum.zip(Stream.iterate(0, &(&1 + 2)))
    |> Enum.map(fn {actual, expected} -> abs(actual - expected) end)
    |> Enum.sum()
  end
end

p448.ex

defmodule RWC_448 do
  @moduledoc """
  You're given a 2D grid representing a city where each cell is either empty
  (`0`), a fire station (`1`), or a building (`2`). Return a 2D grid where each
  cell shows the minimum distance to the nearest fire station.

  iex> RWC_448.fire_station_coverage([[2, 0, 1], [0, 2, 0], [1, 0, 2]])
  [[2, 1, 0], [1, 2, 1], [0, 1, 2]]

  iex> RWC_448.fire_station_coverage([
  ...>   [1, 0, 0, 1],
  ...>   [0, 0, 0, 0],
  ...>   [0, 0, 0, 0],
  ...>   [1, 0, 0, 1]
  ...> ])
  [
    [0, 1, 1, 0],
    [1, 2, 2, 1],
    [1, 2, 2, 1],
    [0, 1, 1, 0]
  ]
  """

  def fire_station_coverage(grid) do
    rows = length(grid)
    cols = grid |> hd() |> length()

    stations =
      for {row, r} <- Enum.with_index(grid),
          {1, c} <- Enum.with_index(row),
          do: {r, c}

    distances =
      bfs(:queue.from_list(stations), Map.new(stations, &{&1, 0}), rows, cols)

    for r <- 0..(rows - 1), do: for(c <- 0..(cols - 1), do: distances[{r, c}])
  end

  defp bfs(queue, distances, rows, cols) do
    case :queue.out(queue) do
      {{:value, point}, queue} ->
        point
        |> neighbors(rows, cols)
        |> Enum.reject(&Map.has_key?(distances, &1))
        |> Enum.reduce({queue, distances}, fn next, {queue, distances} ->
          {:queue.in(next, queue),
           Map.put(distances, next, distances[point] + 1)}
        end)
        |> then(fn {queue, distances} -> bfs(queue, distances, rows, cols) end)

      {:empty, _queue} ->
        distances
    end
  end

  defp neighbors({r, c}, rows, cols) do
    [{r - 1, c}, {r + 1, c}, {r, c - 1}, {r, c + 1}]
    |> Enum.filter(fn {r, c} -> r in 0..(rows - 1) and c in 0..(cols - 1) end)
  end
end

p449.ex

defmodule RWC_449 do
  @moduledoc """
  Given a text string and a pattern, implement a fuzzy string search that finds
  all positions in the text where the pattern matches with at most `k` errors.

  iex> RWC_449.fuzzy_search("the cat sat on the mat", "cat", 0)
  [%{position: 4, errors: 0}]

  iex> RWC_449.fuzzy_search("cassidoo", "cool", 1)
  []
  """

  def fuzzy_search(text, pattern, max_errors) do
    text = String.graphemes(text)
    pattern = String.graphemes(pattern)
    text_length = length(text)
    pattern_length = length(pattern)

    0..(text_length - 1)//1
    |> Enum.flat_map(fn index ->
      max(1, pattern_length - max_errors)..min(
        text_length - index,
        pattern_length + max_errors
      )//1
      |> Enum.map(fn length -> {index, Enum.slice(text, index, length)} end)
    end)
    |> Enum.map(fn {index, piece} -> {index, edit_distance(piece, pattern)} end)
    |> Enum.filter(fn {_index, errors} -> errors <= max_errors end)
    |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
    |> Enum.map(fn {index, errors} ->
      %{position: index, errors: Enum.min(errors)}
    end)
    |> Enum.sort_by(& &1.position)
  end

  defp edit_distance(left, right) do
    initial = Enum.to_list(0..length(right))

    left
    |> Enum.with_index(1)
    |> Enum.reduce(initial, fn {char, row}, previous ->
      right
      |> Enum.with_index(1)
      |> Enum.reduce([row], fn {other, column}, current ->
        insert = hd(current) + 1
        delete = Enum.at(previous, column) + 1

        replace =
          Enum.at(previous, column - 1) + if(char == other, do: 0, else: 1)

        [min(insert, min(delete, replace)) | current]
      end)
      |> Enum.reverse()
    end)
    |> List.last()
  end
end

p450.ex

defmodule RWC_450 do
  @moduledoc """
  You are given a file system represented as a map where keys are absolute paths
  and values are either `nil` (real file/directory) or a string (a symlink
  pointing to another path). Resolve a given path to its real destination,
  following symlinks along the way.

  iex> fs = %{
  ...>   "/a" => "/b",
  ...>   "/b" => "/c",
  ...>   "/c" => nil,
  ...>   "/loop1" => "/loop2",
  ...>   "/loop2" => "/loop1",
  ...>   "/real" => nil,
  ...>   "/alias" => "/real"
  ...> }
  ...> RWC_450.resolve_path(fs, "/a")
  "/c"

  iex> fs = %{
  ...>   "/a" => "/b",
  ...>   "/b" => "/c",
  ...>   "/c" => nil,
  ...>   "/loop1" => "/loop2",
  ...>   "/loop2" => "/loop1",
  ...>   "/real" => nil,
  ...>   "/alias" => "/real"
  ...> }
  ...> RWC_450.resolve_path(fs, "/alias")
  "/real"

  iex> fs = %{
  ...>   "/a" => "/b",
  ...>   "/b" => "/c",
  ...>   "/c" => nil,
  ...>   "/loop1" => "/loop2",
  ...>   "/loop2" => "/loop1",
  ...>   "/real" => nil,
  ...>   "/alias" => "/real"
  ...> }
  ...> RWC_450.resolve_path(fs, "/loop1")
  nil

  iex> fs = %{
  ...>   "/a" => "/b",
  ...>   "/b" => "/c",
  ...>   "/c" => nil,
  ...>   "/loop1" => "/loop2",
  ...>   "/loop2" => "/loop1",
  ...>   "/real" => nil,
  ...>   "/alias" => "/real"
  ...> }
  ...> RWC_450.resolve_path(fs, "/real")
  "/real"
  """

  def resolve_path(fs, path), do: resolve_path(fs, path, MapSet.new())

  defp resolve_path(fs, path, seen) do
    cond do
      MapSet.member?(seen, path) -> nil
      Map.get(fs, path) == nil and Map.has_key?(fs, path) -> path
      is_binary(fs[path]) -> resolve_path(fs, fs[path], MapSet.put(seen, path))
      true -> nil
    end
  end
end

p451.ex

defmodule RWC_451 do
  @moduledoc """
  Given an integer `n`, return all unique combinations of Perrin numbers (up to
  and including the `n`th Perrin number) that sum to a target value `k`, where
  each Perrin number can be used at most once.

  iex> RWC_451.perrin_combinations(7, 12)
  [[0, 2, 3, 7], [0, 5, 7], [2, 3, 7], [5, 7]]

  iex> RWC_451.perrin_combinations(6, 5)
  [[0, 2, 3], [0, 5], [2, 3], [5]]
  """

  def perrin_combinations(n, target) do
    0..n
    |> Enum.map(&perrin/1)
    |> Enum.uniq()
    |> Enum.sort()
    |> combinations(target)
  end

  defp combinations(nums, target), do: combinations(nums, target, [])

  defp combinations(_nums, 0, combo), do: [Enum.reverse(combo)]
  defp combinations([], _target, _combo), do: []

  defp combinations([num | rest], target, combo) when num <= target do
    combinations(rest, target - num, [num | combo]) ++
      combinations(rest, target, combo)
  end

  defp combinations([_num | rest], target, combo),
    do: combinations(rest, target, combo)

  defp perrin(0), do: 3
  defp perrin(1), do: 0
  defp perrin(2), do: 2
  defp perrin(n), do: perrin(n - 2) + perrin(n - 3)
end

p452.ex

defmodule RWC_452 do
  @moduledoc """
  You're building a pizza ordering system that enforces strict ingredient
  layering rules. Given pizza layers (bottom to top) and rules where ingredient
  A must appear below ingredient B, return the first violated pair or `true`.

  iex> layers = ["dough", "sauce", "cheese", "pepperoni", "basil"]
  ...> rules = [
  ...>   ["sauce", "cheese"],
  ...>   ["cheese", "pepperoni"],
  ...>   ["dough", "basil"]
  ...> ]
  ...> RWC_452.validate_pizza(layers, rules)
  true

  iex> layers = ["dough", "sauce", "cheese", "pepperoni", "basil"]
  ...> rules = [["cheese", "pepperoni"], ["cheese", "sauce"]]
  ...> RWC_452.validate_pizza(layers, rules)
  ["cheese", "sauce"]
  """

  def validate_pizza(layers, rules) do
    positions = layers |> Enum.with_index() |> Map.new()

    Enum.find_value(rules, true, fn [below, above] ->
      if positions[below] < positions[above], do: false, else: [below, above]
    end)
  end
end

p453.ex

defmodule RWC_453 do
  @moduledoc """
  Given a string containing letters and `?` wildcards, and a target pattern
  string, rearrange the entire string however you like. Return the maximum
  number of non-overlapping copies of `pattern` that can appear in the
  rearranged result.

  iex> RWC_453.max_pattern_copies("abcabc???", "ac")
  3

  iex> RWC_453.max_pattern_copies("aab??", "aab")
  1

  iex> RWC_453.max_pattern_copies("??????", "abc")
  2
  """

  def max_pattern_copies(str, pattern) do
    chars = frequencies(str)
    pattern = pattern |> String.graphemes() |> Enum.frequencies()

    0..String.length(str)
    |> Enum.take_while(&possible?(&1, chars, pattern))
    |> List.last()
  end

  defp possible?(count, chars, pattern) do
    missing =
      pattern
      |> Enum.map(fn {char, needed} ->
        max(0, needed * count - Map.get(chars, char, 0))
      end)
      |> Enum.sum()

    missing <= Map.get(chars, "?", 0)
  end

  defp frequencies(str), do: str |> String.graphemes() |> Enum.frequencies()
end

p454.ex

defmodule RWC_454 do
  @moduledoc """
  You are given a 2D grid where `1` represents an intact tile and `0` represents
  a broken tile. Find the minimum number of tiles you need to repair to ensure
  no broken region has an area larger than `k`.

  iex> grid = [[1, 0, 0, 1], [1, 0, 0, 1], [1, 1, 0, 1], [0, 1, 1, 1]]
  ...> RWC_454.min_repairs(grid, 2)
  2

  iex> grid = [[1, 0, 0, 1], [1, 0, 0, 1], [1, 1, 0, 1], [0, 0, 1, 1]]
  ...> RWC_454.min_repairs(grid, 1)
  3
  """

  def min_repairs(grid, max_size) do
    grid
    |> regions()
    |> Enum.map(&repairs_for(&1, max_size))
    |> Enum.sum()
  end

  defp repairs_for(region, max_size) when length(region) <= max_size, do: 0

  defp repairs_for(region, max_size) do
    1..length(region)
    |> Enum.find(fn count ->
      region
      |> combinations(count)
      |> Enum.any?(&valid_repair?(region, &1, max_size))
    end)
  end

  defp valid_repair?(region, repaired, max_size) do
    remaining = MapSet.difference(MapSet.new(region), MapSet.new(repaired))

    remaining
    |> connected_sizes()
    |> Enum.all?(&(&1 <= max_size))
  end

  defp regions(grid) do
    zeros =
      for {row, r} <- Enum.with_index(grid),
          {0, c} <- Enum.with_index(row),
          into: MapSet.new() do
        {r, c}
      end

    find_regions(zeros, [])
  end

  defp find_regions(zeros, regions) do
    case Enum.at(zeros, 0) do
      nil ->
        regions

      point ->
        region = connected(zeros, [point], MapSet.new())

        find_regions(MapSet.difference(zeros, region), [
          MapSet.to_list(region) | regions
        ])
    end
  end

  defp connected_sizes(points),
    do: points |> find_regions([]) |> Enum.map(&length/1)

  defp connected(_points, [], seen), do: seen

  defp connected(points, [point | queue], seen) do
    point
    |> neighbors()
    |> Enum.filter(
      &(MapSet.member?(points, &1) and not MapSet.member?(seen, &1))
    )
    |> then(&connected(points, queue ++ &1, MapSet.put(seen, point)))
  end

  defp neighbors({r, c}), do: [{r - 1, c}, {r + 1, c}, {r, c - 1}, {r, c + 1}]

  defp combinations(_items, 0), do: [[]]
  defp combinations([], _count), do: []

  defp combinations([item | rest], count) do
    Enum.map(combinations(rest, count - 1), &[item | &1]) ++
      combinations(rest, count)
  end
end

p455.ex

defmodule RWC_455 do
  @moduledoc """
  Given an array of positive integers, find the length of the longest
  subsequence where every adjacent pair of elements in the subsequence is
  coprime.

  iex> RWC_455.longest_coprime_subsequence([6, 12, 4, 8])
  1

  iex> RWC_455.longest_coprime_subsequence([4, 3, 6, 9, 7, 2])
  4
  """

  def longest_coprime_subsequence(nums) do
    nums
    |> Enum.with_index()
    |> Enum.reduce([], fn {num, index}, lengths ->
      best =
        nums
        |> Enum.take(index)
        |> Enum.with_index()
        |> Enum.filter(fn {prev, _prev_index} ->
          Integer.gcd(prev, num) == 1
        end)
        |> Enum.map(fn {_prev, prev_index} ->
          Enum.at(lengths, prev_index) + 1
        end)
        |> Enum.max(fn -> 1 end)

      lengths ++ [best]
    end)
    |> Enum.max()
  end
end

p456.ex

defmodule RWC_456 do
  @moduledoc """
  You are given a 2D grid size, a starting position for a bouncing object, a
  target position, and an initial direction. On each step, the object moves one
  cell diagonally, and if its next move would leave the grid, it bounces by
  reversing the corresponding direction.

  iex> RWC_456.count_bounces_to_target([8, 8], [0, 0], [3, 4], [1, 4])
  2

  iex> RWC_456.count_bounces_to_target([3, 3], [0, 1], [2, 1], [1, 1])
  1

  iex> RWC_456.count_bounces_to_target([4, 5], [0, 0], [3, 3], [1, 1])
  0
  """

  def count_bounces_to_target(size, start, target, velocity) do
    move(
      List.to_tuple(size),
      List.to_tuple(start),
      List.to_tuple(target),
      List.to_tuple(velocity),
      0
    )
  end

  defp move(_size, point, point, _velocity, bounces), do: bounces

  defp move({rows, cols} = size, {r, c}, target, {dr, dc}, bounces) do
    {dr, row_bounce} = bounce(r + dr, dr, rows)
    {dc, col_bounce} = bounce(c + dc, dc, cols)

    move(
      size,
      {r + dr, c + dc},
      target,
      {dr, dc},
      bounces + row_bounce + col_bounce
    )
  end

  defp bounce(next, delta, limit) when next < 0 or next >= limit,
    do: {-delta, 1}

  defp bounce(_next, delta, _limit), do: {delta, 0}
end

p457.ex

defmodule RWC_457 do
  @moduledoc """
  Given a string consisting of letters, convert each character to its opposite
  case. When the alternating option is true, alternate character case instead.

  iex> RWC_457.toggle_char("Hello, world!")
  "hELLO, WORLD!"

  iex> RWC_457.toggle_char("HeheHeheHEheheHeH")
  "hEHEhEHEheHEHEhEh"

  iex> RWC_457.toggle_char("This will be alternated", true)
  "ThIs WiLl Be AlTeRnAtEd"
  """

  def toggle_char(str, alternating \\ false)

  def toggle_char(str, false) do
    str
    |> String.graphemes()
    |> Enum.map(&swap_case/1)
    |> Enum.join()
  end

  def toggle_char(str, true) do
    str
    |> String.graphemes()
    |> Enum.reduce({[], 0}, fn char, {chars, index} ->
      cond do
        not letter?(char) -> {[char | chars], index}
        rem(index, 2) == 0 -> {[String.upcase(char) | chars], index + 1}
        true -> {[String.downcase(char) | chars], index + 1}
      end
    end)
    |> elem(0)
    |> Enum.reverse()
    |> Enum.join()
  end

  defp swap_case(char) do
    cond do
      char =~ ~r/[a-z]/ -> String.upcase(char)
      char =~ ~r/[A-Z]/ -> String.downcase(char)
      true -> char
    end
  end

  defp letter?(char), do: char =~ ~r/[A-Za-z]/
end

p458.ex

defmodule RWC_458 do
  @moduledoc """
  Given a queue of customer names and an integer `n`, move every `n`th customer
  to the end of the line while preserving relative order otherwise.

  iex> RWC_458.shuffle_line(["Ada", "Ben", "Cam", "Diya", "Eli", "Fay"], 3)
  ["Ada", "Ben", "Diya", "Eli", "Cam", "Fay"]

  iex> RWC_458.shuffle_line(["A", "B", "C", "D", "E"], 2)
  ["A", "C", "E", "B", "D"]

  iex> RWC_458.shuffle_line(["Mo", "Noah", "Oli"], 1)
  ["Mo", "Noah", "Oli"]
  """

  def shuffle_line(customers, count) do
    customers
    |> Enum.with_index(1)
    |> Enum.split_with(fn {_customer, index} -> rem(index, count) != 0 end)
    |> then(fn {kept, moved} -> Enum.map(kept ++ moved, &elem(&1, 0)) end)
  end
end

p459.ex

defmodule RWC_459 do
  @moduledoc """
  Given an array of object weights and an array of suitcase capacities,
  determine the minimum number of suitcases needed to pack all objects. Return
  `-1` if it is impossible.

  iex> RWC_459.pack_suitcases([4, 8, 1, 4, 2], [10, 6, 8])
  3

  iex> RWC_459.pack_suitcases([9, 7, 6], [10, 6])
  -1
  """

  def pack_suitcases(weights, capacities) do
    weights = Enum.sort(weights, :desc)
    capacities = Enum.sort(capacities, :desc)

    1..length(capacities)
    |> Enum.find(fn count ->
      capacities
      |> combinations(count)
      |> Enum.any?(&packable?(weights, &1))
    end)
    |> then(&(&1 || -1))
  end

  defp packable?(weights, capacities),
    do: packable?(weights, capacities, MapSet.new())

  defp packable?([], _capacities, _seen), do: true

  defp packable?([weight | rest], capacities, seen) do
    key = {weights_key([weight | rest]), capacities}

    cond do
      MapSet.member?(seen, key) ->
        false

      true ->
        capacities
        |> Enum.with_index()
        |> Enum.filter(fn {capacity, _index} -> capacity >= weight end)
        |> Enum.any?(fn {capacity, index} ->
          next_capacities =
            List.replace_at(capacities, index, capacity - weight)
            |> Enum.sort(:desc)

          packable?(rest, next_capacities, MapSet.put(seen, key))
        end)
    end
  end

  defp weights_key(weights), do: Enum.join(weights, ",")

  defp combinations(_items, 0), do: [[]]
  defp combinations([], _count), do: []

  defp combinations([item | rest], count) do
    Enum.map(combinations(rest, count - 1), &[item | &1]) ++
      combinations(rest, count)
  end
end