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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,143 @@ | ||
| defmodule AdventOfCode.Y2023.Day22 do | ||
| @moduledoc """ | ||
| --- Day 22: Sand Slabs --- | ||
| Problem Link: https://adventofcode.com/2023/day/22 | ||
| Difficulty: xl | ||
| Tags: stack range not-fast-enough | ||
| """ | ||
| alias AdventOfCode.Helpers.{InputReader, Transformers} | ||
|
|
||
| def input, do: InputReader.read_from_file(2023, 22) | ||
|
|
||
| def run(input \\ input()) do | ||
| input | ||
| |> parse() | ||
| |> supports() | ||
| |> then(&{length(free(&1)), disintegrate(&1)}) | ||
| end | ||
|
|
||
| def parse(data \\ input()) do | ||
| for {line, i} <- Enum.with_index(Transformers.lines(data)) do | ||
| line | ||
| |> String.split([",", "~"], trim: true) | ||
| |> Enum.map(&String.to_integer/1) | ||
| |> Enum.chunk_every(3) | ||
| |> Enum.zip_with(fn [a, b] -> Range.new(min(a, b), max(a, b)) end) | ||
| |> List.to_tuple() | ||
| |> then(fn {x, y, z} -> {to_alpha(i), x, y, z} end) | ||
| end | ||
| end | ||
|
|
||
| defp supports(data), do: data |> drop() |> support() | ||
| defp to_alpha(i), do: to_alpha(i, []) | ||
| defp to_alpha(i, acc) when i < 26, do: to_string([rem(i, 26) + 65 | acc]) | ||
| defp to_alpha(i, acc), do: to_alpha(div(i, 26) - 1, [rem(i, 26) + 65 | acc]) | ||
|
|
||
| defp drop(bricks), | ||
| do: | ||
| bricks | ||
| |> Enum.sort_by(fn {_, _, _, z1.._} -> z1 end) | ||
| |> drop([]) | ||
|
|
||
| defp drop([], settled), do: settled | ||
|
|
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| defp drop([{_, _, _, 1.._} = brick | bricks], settled), | ||
| do: drop(bricks, [brick | settled]) | ||
|
|
||
| defp drop([{id, ax, ay, az} | bricks], settled) do | ||
| {_, _, _, _..bz2} = | ||
| Enum.filter(settled, fn {_, bx, by, _} -> | ||
| not (Range.disjoint?(ax, bx) or | ||
| Range.disjoint?(ay, by)) | ||
| end) | ||
| |> Enum.max_by( | ||
| fn {_, _, _, _..bz2} -> bz2 end, | ||
| fn -> {nil, nil, nil, 0..0} end | ||
| ) | ||
|
|
||
| az1 = bz2 + 1 | ||
| az2 = bz2 + Range.size(az) | ||
| brick = {id, ax, ay, az1..az2} | ||
|
|
||
| drop(bricks, [brick | settled]) | ||
| end | ||
|
|
||
| defp support(bricks), do: support(bricks, bricks, %{}) | ||
| defp support([], _, supports), do: supports | ||
|
|
||
| defp support([{_, ax, ay, az1.._} = current | rest], bricks, supports) do | ||
| others = | ||
| Enum.filter(bricks, fn {_, bx, by, _..bz2} -> | ||
| bz2 == az1 - 1 and | ||
| not (Range.disjoint?(ax, bx) or | ||
| Range.disjoint?(ay, by)) | ||
| end) | ||
|
|
||
| supports = | ||
| Map.update( | ||
| supports, | ||
| current, | ||
| %{is_above: others, is_below: []}, | ||
| fn %{is_above: above} = existing -> | ||
| %{existing | is_above: others ++ above} | ||
| end | ||
| ) | ||
|
|
||
| supports = | ||
| Enum.reduce(others, supports, fn other, supports -> | ||
| Map.update( | ||
| supports, | ||
| other, | ||
| %{is_above: [], is_below: [current]}, | ||
| fn %{is_below: below} = existing -> | ||
| %{existing | is_below: [current | below]} | ||
| end | ||
| ) | ||
| end) | ||
|
|
||
| support(rest, bricks, supports) | ||
| end | ||
|
|
||
| defp free(supports) do | ||
| supports | ||
| |> Enum.filter(fn {_, %{is_above: is_above}} -> length(is_above) == 1 end) | ||
| |> Enum.flat_map(fn {_, %{is_above: is_above}} -> is_above end) | ||
| |> MapSet.new() | ||
| |> then(fn required -> | ||
| supports | ||
| |> Map.keys() | ||
| |> MapSet.new() | ||
| |> MapSet.difference(required) | ||
| |> Enum.to_list() | ||
| end) | ||
| end | ||
|
|
||
| defp chain(brick, supports), do: chain([brick], supports, MapSet.new()) | ||
| defp chain([], _, acc), do: acc | ||
|
|
||
| defp chain([brick | rest], supports, acc) do | ||
| destroyed = | ||
| supports[brick].is_below | ||
| |> Enum.filter(fn above_brick -> | ||
| below_bricks = supports[above_brick].is_above | ||
|
|
||
| length(below_bricks) == 1 or | ||
| Enum.all?(below_bricks, fn below -> MapSet.member?(acc, below) end) | ||
| end) | ||
|
|
||
| destroyed | ||
| |> MapSet.new() | ||
| |> MapSet.union(acc) | ||
| |> then(fn acc -> chain(rest ++ destroyed, supports, acc) end) | ||
| end | ||
|
|
||
| defp disintegrate(supports) do | ||
| for brick <- Map.keys(supports), reduce: 0 do | ||
| acc -> | ||
| brick | ||
| |> chain(supports) | ||
| |> MapSet.size() | ||
| |> Kernel.+(acc) | ||
| end | ||
| end | ||
| end |
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