Day9

day9/sol.livemd

Divyansh Shrivastava

@divxvid

aoc-2023-elixir

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Day9

Mix.install([
  {:kino, "~> 0.11.3"}
])

Section

input = Kino.Input.textarea("Enter input here:")

defmodule Day9Part1 do
  def solve(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(
      &amp;(String.split(&amp;1, " ", trim: true)
        |> Enum.map(fn x -> String.to_integer(x) end))
    )
    |> Enum.map(&amp;solve_one/1)
    |> Enum.sum()
  end

  defp solve_one(data) do
    next_sequence =
      Enum.zip(data, Enum.slice(data, 1..-1))
      |> Enum.map(fn {a, b} -> b - a end)

    num_non_zeroes = Enum.filter(next_sequence, &amp;(&amp;1 != 0)) |> length()

    case num_non_zeroes do
      0 -> List.last(data)
      _ -> List.last(data) + solve_one(next_sequence)
    end
  end
end

{:module, Day9Part1, <<70, 79, 82, 49, 0, 0, 11, ...>>, {:solve_one, 1}}

input
|> Kino.Input.read()
|> Day9Part1.solve()

1725987467

Part 2

defmodule Day9Part2 do
  def solve(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(
      &amp;(String.split(&amp;1, " ", trim: true)
        |> Enum.map(fn x -> String.to_integer(x) end))
    )
    |> Enum.map(&amp;solve_one/1)
    |> Enum.sum()
  end

  defp solve_one(data) do
    next_sequence =
      Enum.zip(data, Enum.slice(data, 1..-1))
      |> Enum.map(fn {a, b} -> b - a end)

    num_non_zeroes = Enum.filter(next_sequence, &amp;(&amp;1 != 0)) |> length()

    case num_non_zeroes do
      0 -> hd(data)
      _ -> hd(data) - solve_one(next_sequence)
    end
  end
end

{:module, Day9Part2, <<70, 79, 82, 49, 0, 0, 11, ...>>, {:solve_one, 1}}

input
|> Kino.Input.read()
|> Day9Part2.solve()

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