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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,107 @@ | ||
| defmodule AdventOfCode.Y2023.Day23 do | ||
| @moduledoc """ | ||
| --- Day 23: A Long Walk --- | ||
| Problem Link: https://adventofcode.com/2023/day/23 | ||
| Difficulty: xl | ||
| Tags: graph longest-path slow refactor | ||
| """ | ||
| alias AdventOfCode.Helpers.InputReader | ||
| alias AdventOfCode.Algorithms.Grid | ||
|
|
||
| def input, do: InputReader.read_from_file(2023, 23) | ||
|
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| @start {0, 1} | ||
| @up {-1, 0} | ||
| @down {1, 0} | ||
| @left {0, -1} | ||
| @right {0, 1} | ||
| @slopes %{@up => "^", @down => "v", @left => "<", @right => ">"} | ||
|
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| def run(input \\ input()) do | ||
| input = parse(input) | ||
|
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| task_1 = Task.async(fn -> run_1(input) end) | ||
| task_2 = Task.async(fn -> run_2(input) end) | ||
|
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| {Task.await(task_1, :infinity), Task.await(task_2, :infinity)} | ||
| end | ||
|
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| def parse(data \\ input()) do | ||
| grid = Grid.text_to_grid2d(data) | ||
| {max_r, max_c} = Enum.max(Map.keys(grid)) | ||
|
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| {{max_r, max_c - 1}, edges(grid, [{@start, @down}], [])} | ||
| end | ||
|
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| defp run_1({{_, _} = finish, edges}) do | ||
| edges | ||
| |> make_graph() | ||
| |> find_longest_path(@start, finish) | ||
| end | ||
|
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| defp run_2({{_, _} = finish, edges}) do | ||
| edges | ||
| |> make_graph(:directed) | ||
| |> find_longest_path(@start, finish) | ||
| end | ||
|
|
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| defp edges(_, [], es), do: es | ||
|
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| defp edges(g, [{tile, dir} | todo], es) do | ||
| {{tr, tc}, dist, ntodo} = follow_path(g, [{tile, dir}], tile, 0) | ||
| ebgs = es |> Enum.map(fn {p, d, _, _} -> {p, d} end) | ||
| nftodo = Enum.filter(ntodo, fn {p, d} -> {p, d} not in ebgs and {p, d} not in todo end) | ||
|
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| edges(g, todo ++ nftodo, [{tile, dir, {tr, tc}, dist} | es]) | ||
| end | ||
|
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| defp make_graph(edges, type \\ :undirected) do | ||
| for {f, _, t, w} <- edges, reduce: Graph.new() do | ||
| acc -> | ||
| acc | ||
| |> Graph.add_edge(f, t, weight: w) | ||
| |> then(fn graph -> | ||
| (type == :directed && Graph.add_edge(graph, t, f, weight: w)) || graph | ||
| end) | ||
| end | ||
| end | ||
|
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| defp follow_path(g, [{tile, dir}], _, n) do | ||
| next_tile = follow(tile, dir) | ||
|
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| if next_tile in Map.keys(g) do | ||
| dirs = | ||
| [@up, @down, @left, @right] | ||
| |> List.delete(opposite(dir)) | ||
| |> Enum.map(fn d -> {d, g[follow(next_tile, d)]} end) | ||
| |> Enum.filter(fn {_, c} -> c != "#" and c != nil end) | ||
|
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| dirs | ||
| |> Enum.filter(fn {d, c} -> c == "." or c == @slopes[d] end) | ||
| |> Enum.map(fn {d, _} -> {next_tile, d} end) | ||
| |> then(fn dir -> | ||
| (length(dirs) >= 2 && {next_tile, n + 1, dir}) || | ||
| follow_path(g, dir, next_tile, n + 1) | ||
| end) | ||
| else | ||
| {tile, n, []} | ||
| end | ||
| end | ||
|
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| defp follow_path(_, dir, ppt, n), do: {ppt, n, dir} | ||
| defp follow({a, b}, {c, d}), do: {a + c, b + d} | ||
| defp opposite({a, b}), do: {-a, -b} | ||
|
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| defp path_length([a, b | rest], g, sum) do | ||
| wt = g |> Graph.edge(a, b) |> Map.get(:weight, 0) | ||
| path_length([b | rest], g, sum + wt) | ||
| end | ||
|
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| defp path_length([_], _, sum), do: sum | ||
|
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| defp find_longest_path(graph, start, finish) do | ||
| Graph.Pathfinding.all(graph, start, finish) | ||
| |> Stream.map(&path_length(&1, graph, 0)) | ||
| |> Enum.max() | ||
| end | ||
| end |
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