SpotifyPuzzle.js

const paragraph =
  'If you want to jumpstart the process of talking to us about this role, here’s a little challenge: write a program that outputs the largest unique set of characters that can be removed from this paragraph without letting its length drop below 50.';

// First we'll take the set of unique characters

const uniqueCharacters = str => {
  const chars = [];
  str.split('').forEach(char => {
    if (!chars.includes(char)) {
      chars.push(char);
    }
  });
  return chars;
};

// ...and count the number of times each character can be found in our original text.
// We can then sort them by frequency.

const countAndSortCharacters = characters => {
  const countedChars = {};
  const sortedVals = {};

  characters.forEach(char => {
    let escapedChar = char;
    if (char === '.') {
      escapedChar = '\\.'; // escape period
    }
    countedChars[char] = paragraph.match(new RegExp(escapedChar, 'g')).length;
  });
  Object.keys(countedChars)
    .sort((a, b) => countedChars[a] - countedChars[b])
    .forEach(val => {
      sortedVals[val] = countedChars[val];
    });
  return sortedVals;
};

// Last, we can use a simple regular expression to filter an arbitrary
// list of characters out of a string.

const removeCharacters = (charachters, str) => {
  const reg = new RegExp(charachters.join('|'), 'g');
  return str.replace(reg, '');
};

const uniques = uniqueCharacters(paragraph);
const countedCharacters = countAndSortCharacters(uniques);

console.log(countedCharacters);

// {
//   '0': 1,
//   '5': 1,
//   I: 1,
//   y: 1,
//   j: 1,
//   k: 1,
//   ',': 1,
//   '’': 1,
//   ':': 1,
//   q: 1,
//   v: 1,
//   '.': 1,
//   d: 2,
//   b: 3,
//   f: 4,
//   w: 4,
//   m: 4,
//   c: 5,
//   n: 7,
//   p: 7,
//   g: 7,
//   u: 9,
//   i: 9,
//   l: 10,
//   s: 12,
//   h: 12,
//   o: 15,
//   r: 15,
//   a: 17,
//   e: 20,
//   t: 29,
//   ' ': 42
// }

// By observing this output, we can immediately see that there are several possible answers,
// to this question, but each correct answer is a list of 30 characters:
// we can remove all characters *except* the space character (appearing 42 times) and one other character
// appearing 8 or more times (in the ranked list, that's characters u to t) in order to build the
// largest set of characters that can be removed without the remaining text dropping below 50 characters.
// Thus, there are ten valid answers, all lists 30 characters in length.

// For example:

console.log(
  removeCharacters(
    [
      '0',
      '5',
      'I',
      'y',
      'j',
      'k',
      ',',
      '’',
      ':',
      'q',
      'v',
      '\\.', // escaped period
      'd',
      'b',
      'f',
      'w',
      'm',
      'c',
      'n',
      'p',
      'g',
      'u',
      'i',
      'l',
      's',
      'h',
      'o',
      'r',
      'a',
      'e',
    ],
    paragraph
  ).length
);

// 71