5 votes

Day 25: Sea Cucumber

Automatically posted
Tags: advent of code.2021

Today's problem description: https://adventofcode.com/2021/day/25

Please post your solutions in your own top-level comment. Here's a template you can copy-paste into your comment to format it nicely, with the code collapsed by default inside an expandable section with syntax highlighting (you can replace python with any of the "short names" listed in this page of supported languages):

<details>
<summary>Part 1</summary>

```python
Your code here.
```

</details>

1 comment

  1. jzimbel
    Link
    Elixir Pretty quick and simple. Posting my messy code as-is and going to bed. Merry Christmas, folks. Part 1 defmodule AdventOfCode.Solution.Year2021.Day25 do def part1(input) do {grid, width,...

    Elixir

    Pretty quick and simple. Posting my messy code as-is and going to bed. Merry Christmas, folks.

    Part 1 
    defmodule AdventOfCode.Solution.Year2021.Day25 do
  def part1(input) do
    {grid, width, height} = parse_input(input)

    grid
    |> Stream.iterate(&step(&1, width, height))
    |> Stream.chunk_every(2, 1, :discard)
    |> Stream.with_index(1)
    |> Enum.find(&match?({[grid, grid], _}, &1))
    |> elem(1)
  end

  def part2(_input) do
  end

  defp step(grid, width, height) do
    grid
    |> Enum.into(%{}, fn
      {{x, y}, ?>} = cuke ->
        move_to = {rem(x + 1, width), y}

        case grid[move_to] do
          nil -> {move_to, ?>}
          _ -> cuke
        end

      down ->
        down
    end)
    |> then(fn grid ->
      Enum.into(grid, %{}, fn
        {{x, y}, ?v} = cuke ->
          move_to = {x, rem(y + 1, height)}

          case grid[move_to] do
            nil -> {move_to, ?v}
            _ -> cuke
          end

        right ->
          right
      end)
    end)
  end

  defp parse_input(input) do
    charlists =
      input
      |> String.split()
      |> Enum.map(&String.to_charlist/1)

    height = length(charlists)
    width = length(hd(charlists))

    grid =
      for {line, y} <- Enum.with_index(charlists),
          {char, x} <- Enum.with_index(line),
          char != ?.,
          into: %{},
          do: {{x, y}, char}

    {grid, width, height}
  end
end
    1 vote