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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,80 @@ | ||
| defmodule AdventOfCode.Y2023.Day25 do | ||
| @moduledoc """ | ||
| --- Day 25: Snowverload --- | ||
| Problem Link: https://adventofcode.com/2023/day/25 | ||
| Difficulty: xl | ||
| Tags: graph min-cut probabilistic refactor not-fast-enough | ||
| """ | ||
| alias AdventOfCode.Helpers.{InputReader, Transformers} | ||
|
|
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| def input, do: InputReader.read_from_file(2023, 25) | ||
|
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| def run(input \\ input()) do | ||
| input = parse(input) | ||
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| {run_1(input), run_2(input)} | ||
| end | ||
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| defp run_1(input) do | ||
| Stream.repeatedly(fn -> contract(input) end) | ||
| |> Enum.find(fn g1 -> cut_size(g1, input) == 3 end) | ||
| |> Map.keys() | ||
| |> Enum.map(&String.length/1) | ||
| |> Enum.map(&div(&1, 3)) | ||
| |> Enum.product() | ||
| end | ||
|
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| defp run_2(_), do: "🎉" | ||
|
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| def parse(input) do | ||
| for line <- Transformers.lines(input), reduce: %{} do | ||
| graph -> | ||
| [u | connected] = String.split(line, [":", " "], trim: true) | ||
|
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| for v <- connected, reduce: graph do | ||
| edges -> | ||
| edges | ||
| |> Map.update(u, MapSet.new([v]), &MapSet.put(&1, v)) | ||
| |> Map.update(v, MapSet.new([u]), &MapSet.put(&1, u)) | ||
| end | ||
| end | ||
| end | ||
|
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| def cut_size(g, h) do | ||
| for {key, _} <- g do | ||
| key | ||
| |> String.to_charlist() | ||
| |> Enum.chunk_every(3) | ||
| |> Enum.map(&to_string/1) | ||
| end | ||
| |> then(fn [us, vs] -> | ||
| for u <- us, _ <- MapSet.intersection(h[u], MapSet.new(vs)), reduce: 0 do | ||
| acc -> acc + 1 | ||
| end | ||
| end) | ||
| end | ||
|
|
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| def contract(graph) when map_size(graph) == 2, do: graph | ||
|
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| def contract(graph) do | ||
| {u, u_edges} = Enum.random(graph) | ||
| v = Enum.random(u_edges) | ||
|
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| u_edges = u_edges |> MapSet.delete(v) | ||
| v_edges = graph[v] |> MapSet.delete(u) | ||
| u_v_edges = MapSet.union(u_edges, v_edges) | ||
| uv = u <> v | ||
|
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| Enum.reduce(u_edges, graph, fn c, acc -> | ||
| Map.update!(acc, c, &MapSet.put(MapSet.delete(&1, u), uv)) | ||
| end) | ||
| |> then(fn graph -> | ||
| Enum.reduce(v_edges, graph, fn c, acc -> | ||
| Map.update!(acc, c, &MapSet.put(MapSet.delete(&1, v), uv)) | ||
| end) | ||
| |> Map.drop([u, v]) | ||
| |> Map.put(uv, u_v_edges) | ||
| end) | ||
| |> contract() | ||
| end | ||
| end |
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