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# Day20 ## Untitled   ```elixir {alg, pic} = "input" |> IO.getn(1_000_000) |> String.trim() |> String.split(["\r\n\r\n", "\n\n"], trim: true) |> then(fn [alg, pic] -> {String.replace(alg, ["\n", "\r\n"], ""), pic |> String.split() |> Enum.map(&String.split(&1, "", trim: true))} end) alg = alg |> String.split("", trim: true) |> Enum.with_index() |> Enum.map(fn {k, v} -> {v, (k == "#" && 1) || 0} end) |> Map.new() pic = for {line, row} <- Enum.with_index(pic), {cell, col} <- Enum.with_index(line), into: %{} do {{row, col}, (cell == "#" && 1) || 0} end ```  ```elixir defmodule D20 do import Bitwise def enhance(pic, alg, count, new_pic) do field = count - 1 &&& alg[0] {{min_row, min_col}, {max_row, max_col}} = pic |> Map.keys() |> Enum.min_max() for row <- (min_row - 2)..(max_row + 2), col <- (min_col - 2)..(max_col + 2), into: new_pic do {row, col} |> neighbours |> Enum.map(&Map.get(pic, &1, field)) |> Integer.undigits(2) |> then(fn i -> {{row, col}, alg[i]} end) end end def neighbours({row, col}) do for row_offset <- -1..1, col_offset <- -1..1 do {row + row_offset, col + col_offset} end end def solve(pic, alg, times) do new_pic = Enum.reduce(1..times, pic, fn count, pic -> D20.enhance(pic, alg, count, %{}) end) {{min_row, min_col}, {max_row, max_col}} = new_pic |> Map.keys() |> Enum.min_max() for row <- min_row..max_row do for col <- min_col..max_col do (new_pic[{row, col}] == 1 && "#") || "." end |> IO.puts() end for row <- min_row..max_row, col <- min_col..max_col do new_pic[{row, col}] == 1 end |> Enum.reject(&(!&1)) |> Enum.count() end end ``` ## P1  ```elixir D20.solve(pic, alg, 2) ``` ## P2  ```elixir D20.solve(pic, alg, 50) ```

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