Advent of Code 2023 Day 11

AOC2023Day11.ex

import AOC

aoc 2023, 11 do
  def calculate(input, multiplier) do
    grid = grid(input) |> Map.new()
    {rows, cols} = grid |> Enum.unzip() |> elem(0) |> Enum.unzip()
    row_max = rows |> Enum.max()
    col_max = cols |> Enum.max()
    blank_rows = 0..row_max |> Enum.filter(fn row -> Enum.all?(0..col_max, fn col -> grid[{row, col}] == "." end) end)
    blank_cols = 0..col_max |> Enum.filter(fn col -> Enum.all?(0..row_max, fn row -> grid[{row, col}] == "." end) end)
    galaxies = Enum.filter(grid, fn {_, char} -> char == "#" end) |> Enum.unzip() |> elem(0)
    for i <- 1..Enum.count(galaxies), j <- 1..i, j < i do
      distance(Enum.at(galaxies, i-1), Enum.at(galaxies, j-1), blank_rows, blank_cols, multiplier)
    end |> Enum.sum()
  end

  def p1(input) do
    calculate(input, 2)
  end

  def p2(input) do
    calculate(input, 1_000_000)
  end

  def distance({a, b}, {c, d}, blank_rows, blank_cols, multiplier) do
    [lo_row, hi_row] = [a, c] |> Enum.sort()
    [lo_col, hi_col] = [b, d] |> Enum.sort()
    [blank_rows |> Enum.count(fn row -> lo_row <= row and row <= hi_row end) |> Kernel.*(multiplier-1),
     blank_cols |> Enum.count(fn col -> lo_col <= col and col <= hi_col end) |> Kernel.*(multiplier-1),
     hi_row - lo_row,
     hi_col - lo_col] |> Enum.sum()
  end

  def grid(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.with_index
    |> Enum.flat_map(
      fn {line, row} ->
        line
        |> String.split("", trim: true)
        |> Enum.with_index
        |> Enum.map(fn {char, col} -> {{row, col}, char} end)
      end)
  end
end