hauleth.dev
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2024 day 06
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2024/day06.livemd
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2024/day06.livemd
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<!-- livebook:{"persist_outputs":true} -->
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# Untitled notebook
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```elixir
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Mix.install([:kino_aoc, :arrays])
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```
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## Section
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<!-- livebook:{"attrs":"eyJhc3NpZ25fdG8iOiJwdXp6bGVfaW5wdXQiLCJkYXkiOiI2Iiwic2Vzc2lvbl9zZWNyZXQiOiJBRFZFTlRfT0ZfQ09ERV9TRVNTSU9OIiwieWVhciI6IjIwMjQifQ","chunks":null,"kind":"Elixir.KinoAOC.HelperCell","livebook_object":"smart_cell"} -->
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```elixir
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{:ok, puzzle_input} =
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KinoAOC.download_puzzle("2024", "6", System.fetch_env!("LB_ADVENT_OF_CODE_SESSION"))
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```
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<!-- livebook:{"output":true} -->
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```
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{:ok,
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"...#..................#...................#......................#..............................#.............................#...\n....#.......................#........#.#..............##...........#.....#..........#..........................#..................\n.............#........................................................................#.........#.#..#..#..........#..............\n..........#.......#..........#..................#........##...................#..............#....................................\n....................#..........................................................#..#.....................................#.........\n....#............................#..............................................#.....................#..........##....#..........\n.......#.............#......................................................................#.............#.........#.............\n....###......................#....#...........#.....#................................#..........................#.................\n..........#..#...........#..#........................................................#.....#...........#................#.........\n..#....#......#....#....#...................................................................#.....................................\n....................#............#............................................#......#....#...............................#.......\n..........#.......#.........#.......#.............................................................................................\n.......#...#.......................................#...................#..........................................................\n.......#........#............................#.....#.......#..............................................#..................#...#\n.....................#.................................#................#...#...............#.....#.#..........................#..\n.....#..........................................#......................#.............##..............................#........#...\n.....#......#.........................#..........................#..........................................................#..#..\n.#......#.............#......#.................................................#.....#...................##......#................\n.............................................................................##...................................................\n........................................#.......................................#........#.............................#.#.......#\n...........#.....................................#.............................#......#......#..#....................#..#.........\n.............................................#.......................#..................##....#.....#.............................\n........................#..............................................................#..........................................\n#..............#.........................#........#...#...............#..............#..................#....................##...\n...#...#.............................#.......#................................................#........................#....#.....\n.....#.........................#..#.......................#..........#.....................#..................#.#.....#...........\n..................#........#..#.......#...................................................................................#....#..\n..#...#...............................................#.#..#........................................................#....#......#.\n...............#...............#..........................#............................#..........#.............#.................\n............#.....#........#.........................................................#........#........#.....#........#......#....\n............................#.........#....#........#.....#...#.............#.................................#...................\n........#..................#....#.." <> ...}
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```
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```elixir
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map =
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puzzle_input
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|> String.split("\n", trim: true)
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|> Enum.with_index()
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|> Enum.flat_map(fn {row, y} ->
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row
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|> String.to_charlist()
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|> Enum.with_index()
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|> Enum.map(fn {v, x} -> {{y, x}, v} end)
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end)
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|> Map.new()
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```
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<!-- livebook:{"output":true} -->
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```
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%{
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{18, 103} => 46,
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{76, 13} => 46,
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{61, 121} => 46,
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{37, 47} => 46,
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{65, 63} => 46,
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{77, 129} => 46,
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{120, 47} => 46,
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{38, 2} => 46,
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{1, 26} => 46,
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{116, 69} => 46,
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{124, 56} => 46,
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{83, 76} => 46,
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{117, 125} => 46,
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{32, 15} => 46,
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{103, 106} => 46,
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{30, 113} => 46,
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{123, 104} => 46,
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{124, 60} => 46,
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{89, 14} => 46,
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{35, 30} => 46,
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{37, 53} => 46,
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{4, 5} => 46,
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{8, 50} => 46,
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{78, 98} => 46,
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{101, 62} => 46,
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{95, 56} => 46,
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{74, 12} => 46,
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{102, 74} => 46,
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{11, 39} => 46,
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{65, 43} => 46,
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{22, 38} => 46,
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{14, 86} => 46,
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{49, 117} => 46,
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{20, 41} => 46,
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{29, 25} => 46,
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{86, 10} => 46,
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{83, 36} => 46,
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{29, 26} => 46,
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{47, 27} => 46,
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{4, 81} => 46,
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{31, 42} => 46,
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{9, 34} => 46,
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{13, 124} => 46,
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{90, 0} => 46,
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{14, 122} => 46,
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{120, 42} => 46,
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{121, 77} => 46,
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{103, 39} => 46,
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{102, ...} => 46,
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{...} => 46,
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...
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}
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```
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```elixir
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{start_pos, _} = start = Enum.find(map, fn {_pos, v} -> v in ~c'^>v<' end)
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map = Map.replace(map, start_pos, ?.)
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start
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```
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<!-- livebook:{"output":true} -->
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```
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{{93, 71}, 94}
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```
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```elixir
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defmodule Guard do
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def walk(map, start),
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do: walk(map, start, MapSet.new())
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defp walk(map, {pos, dir} = curr, visited) do
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if curr in visited do
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:loop
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else
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visited = MapSet.put(visited, curr)
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case Map.fetch(map, next(pos, dir)) do
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{:ok, ?#} ->
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walk(map, {pos, turn(dir)}, visited)
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{:ok, ?.} ->
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walk(map, {next(pos, dir), dir}, visited)
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:error ->
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MapSet.new(visited, fn {pos, _} -> pos end)
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end
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end
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end
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defp next({y, x}, ?^), do: {y - 1, x}
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defp next({y, x}, ?>), do: {y, x + 1}
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defp next({y, x}, ?v), do: {y + 1, x}
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defp next({y, x}, ?<), do: {y, x - 1}
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defp turn(?^), do: ?>
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defp turn(?>), do: ?v
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defp turn(?v), do: ?<
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defp turn(?<), do: ?^
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end
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```
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<!-- livebook:{"output":true} -->
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```
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{:module, Guard, <<70, 79, 82, 49, 0, 0, 12, ...>>, {:turn, 1}}
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```
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## Part 1
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```elixir
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orig_path = Guard.walk(map, start)
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MapSet.size(orig_path)
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```
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<!-- livebook:{"output":true} -->
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```
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4433
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```
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## Part 2
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```elixir
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orig_path
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|> MapSet.delete(start_pos)
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|> Task.async_stream(fn point ->
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map
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|> Map.put(point, ?#)
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|> Guard.walk(start)
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|> Kernel.==(:loop)
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end, ordered: false)
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|> Enum.count(& &1)
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```
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<!-- livebook:{"output":true} -->
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```
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```
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<!-- livebook:{"offset":7387,"stamp":{"token":"XCP.Wj_YFc-zYzAPEIaLCGnT6vtMYoDgv-DJ3xiuAVdHZPkMwNpP5jrmLW4LBe4lzRgNN75xF-FYACOKdzd82Z71i5y8yC5Wmd072w6qDXxmygH8fZvTOAZM02UZvvg20b5Yhv0","version":2}} -->