commit 90dd84ae8d3f18fea82e67e9997246ab6cb6845c · hauleth.dev/advent-of-code

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2025/day08.livemd
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       # Day 08

     

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       ```elixir

     

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       Mix.install([:kino_aoc])

     

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       ```

     

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       ## Parse

     

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       <!-- livebook:{"attrs":"eyJhc3NpZ25fdG8iOiJwdXp6bGVfaW5wdXQiLCJkYXkiOiI4Iiwic2Vzc2lvbl9zZWNyZXQiOiJBRFZFTlRfT0ZfQ09ERV9TRVNTSU9OIiwieWVhciI6IjIwMjUifQ","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("2025", "8", System.fetch_env!("LB_ADVENT_OF_CODE_SESSION"))

     

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       ```

     

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       ```elixir

     

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       boxes =

     

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         puzzle_input

     

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         |> String.split()

     

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         |> Enum.map(fn raw ->

     

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           raw

     

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           |> String.split(",")

     

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           |> Enum.map(&String.to_integer/1)

     

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           |> List.to_tuple()

     

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         end)

     

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         |> Enum.sort()

     

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       ```

     

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       ## Setup

     

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       ```elixir

     

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       defmodule JunctionBoxes do

     

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         def all_pairs([]), do: []

     

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         def all_pairs([x | rest]) do

     

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           for(y <- rest, do: {x, y}) ++ all_pairs(rest)

     

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         end

     

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         def dist2({ax, ay, az}, {bx, by, bz}) do

     

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           dx = ax - bx

     

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           dy = ay - by

     

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           dz = az - bz

     

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           dx ** 2 + dy ** 2 + dz ** 2

     

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         end

     

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         def group([], {a, b}), do: [MapSet.new([a, b])]

     

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         def group([set | rest], {a, b}) do

     

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           cond do

     

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             a in set and b in set -> [set | rest]

     

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             a in set or b in set -> set |> MapSet.put(a) |> MapSet.put(b) |> do_squash(rest, a, b, [])

     

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             true -> [set | group(rest, {a, b})]

     

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           end

     

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         end

     

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         defp do_squash(curr, [], _, _, acc), do: [curr | acc]

     

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         defp do_squash(curr, [x | rest], a, b, acc) do

     

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           if a in x or b in x do

     

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             [MapSet.union(curr, x) | acc ++ rest]

     

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           else

     

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             do_squash(curr, rest, a, b, [x | acc])

     

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           end

     

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         end

     

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       end

     

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       ```

     

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       ```elixir

     

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       sorted_pairs =

     

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         JunctionBoxes.all_pairs(boxes)

     

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         |> Enum.sort_by(fn {a, b} -> JunctionBoxes.dist2(a, b) end)

     

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       ```

     

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       <!-- livebook:{"branch_parent_index":1} -->

     

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       ## Part 1

     

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       ```elixir

     

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       sorted_pairs

     

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       |> Enum.take(1000)

     

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       |> Enum.reduce([], &JunctionBoxes.group(&2, &1))

     

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       |> Enum.map(&MapSet.size/1)

     

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       |> Enum.sort(:desc)

     

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       |> Enum.take(3)

     

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       |> Enum.product()

     

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       ```

     

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       <!-- livebook:{"branch_parent_index":1} -->

     

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       ## Part 2

     

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       ```elixir

     

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       box_count = length(boxes)

     

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       ```

     

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       ```elixir

     

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       {a, b} =

     

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         sorted_pairs

     

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         |> Enum.reduce_while([], fn pair, acc ->

     

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           new_acc = JunctionBoxes.group(acc, pair)

     

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           if MapSet.size(hd(new_acc)) == box_count do

     

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             {:halt, pair}

     

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           else

     

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             {:cont, new_acc}

     

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           end

     

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         end)

     

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       ```

     

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       ```elixir

     

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       {ax, _, _} = a

     

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       {bx, _, _} = b

     

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       ax * bx

     

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       ```

     

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       <!-- livebook:{"offset":2222,"stamp":{"token":"XCP.sY5bJOGXuU_ZotobOVN6-zcg0TDJGEWVaJESs_-qDHzeEplFoStZ8_c6TRpS5eVpqnzoaj-gsLs_drksuYvMCDcM3T7_M6p9s09DRSKgMU2YB_Ogb0CB6_gAZamF2zEIUw","version":2}} -->