Aurélien Geron
103 lines
2.4 KiB
Elixir
103 lines
2.4 KiB
Elixir
defmodule Aoc2024.Day04 do
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def parse(input) do
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input |> String.split("\n", trim: true) |> Enum.map(&String.graphemes/1)
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end
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defp size(grid) do
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height = length(grid)
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width = grid |> Enum.map(&length/1) |> Enum.max()
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{height, width}
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end
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def part1(grid) do
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word_chars = "XMAS" |> String.graphemes()
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{height, width} = grid |> size()
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-1..1
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|> Enum.map(fn dy ->
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-1..1
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|> Enum.map(fn dx ->
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if dx == 0 && dy == 0 do
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0
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else
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0..(height - 1)
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|> Enum.map(fn y ->
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0..(width - 1)
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|> Enum.map(fn x ->
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all_chars_ok =
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word_chars
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|> Enum.with_index()
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|> Enum.all?(fn {char, index} ->
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cy = y + index * dy
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cx = x + index * dx
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cond do
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cy < 0 ->
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false
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cx < 0 ->
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false
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cy >= height ->
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false
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true ->
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row = grid |> Enum.at(cy)
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if cx >= length(row) do
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false
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else
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row |> Enum.at(cx) == char
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end
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end
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end)
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if all_chars_ok do
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1
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else
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0
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end
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end)
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|> Enum.sum()
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end)
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|> Enum.sum()
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end
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end)
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|> Enum.sum()
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end)
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|> Enum.sum()
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end
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def part2(grid) do
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{height, width} = grid |> size()
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0..(height - 3)
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|> Enum.map(fn y ->
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0..(width - 3)
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|> Enum.map(fn x ->
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center = grid |> Enum.at(y + 1) |> Enum.at(x + 1)
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upper_left = grid |> Enum.at(y) |> Enum.at(x)
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lower_right = grid |> Enum.at(y + 2) |> Enum.at(x + 2)
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upper_right = grid |> Enum.at(y) |> Enum.at(x + 2)
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lower_left = grid |> Enum.at(y + 2) |> Enum.at(x)
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diag1? =
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(upper_left == "M" && lower_right == "S") ||
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(upper_left == "S" && lower_right == "M")
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diag2? =
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(upper_right == "M" && lower_left == "S") ||
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(upper_right == "S" && lower_left == "M")
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if center == "A" && diag1? && diag2? do
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1
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else
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0
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end
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end)
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|> Enum.sum()
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end)
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|> Enum.sum()
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end
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end
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