commit ecbbff549743cfb285ffbad426d8ce1a5ce04424 · hauleth.dev/advent-of-code

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2024/day11.livemd
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       <!-- livebook:{"persist_outputs":true} -->

     

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       # Day 11

     

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       ```elixir

     

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       Mix.install([:kino_aoc])

     

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       ```

     

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       ## Section

     

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       <!-- livebook:{"attrs":"eyJhc3NpZ25fdG8iOiJwdXp6bGVfaW5wdXQiLCJkYXkiOiIxMSIsInNlc3Npb25fc2VjcmV0IjoiQURWRU5UX09GX0NPREVfU0VTU0lPTiIsInllYXIiOiIyMDI0In0","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", "11", System.fetch_env!("LB_ADVENT_OF_CODE_SESSION"))

     

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       ```

     

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       ```

     

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       {:ok, "554735 45401 8434 0 188 7487525 77 7"}

     

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       ```

     

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       ```elixir

     

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       # puzzle_input = "125 17"

     

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       stones =

     

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         puzzle_input

     

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         |> String.split()

     

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

     

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         |> Enum.frequencies()

     

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       ```

     

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       ```

     

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       %{0 => 1, 7 => 1, 77 => 1, 188 => 1, 8434 => 1, 45401 => 1, 554735 => 1, 7487525 => 1}

     

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       ```

     

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       ```elixir

     

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       defmodule Stones do

     

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         def blink(list), do: Enum.reduce(list, %{}, &alter/2)

     

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         defp alter({0, count}, map), do: update(map, 1, count)

     

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         defp alter({n, count}, map) do

     

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           len = len(n)

     

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           if rem(len, 2) == 0 do

     

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             half = 10 ** div(len, 2)

     

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             map

     

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             |> update(div(n, half), count)

     

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             |> update(rem(n, half), count)

     

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           else

     

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             update(map, n * 2024, count)

     

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           end

     

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         end

     

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         defp len(n) when n < 10, do: 1

     

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         defp len(n) when n < 100, do: 2

     

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         defp len(n) when n < 1000, do: 3

     

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         defp len(n) when n < 10000, do: 4

     

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         defp len(n), do: ceil(:math.log10(n))

     

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         defp update(map, key, val), do: Map.update(map, key, val, &(&1 + val))

     

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       end

     

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       ```

     

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       ```

     

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       {:module, Stones, <<70, 79, 82, 49, 0, 0, 11, ...>>, {:update, 3}}

     

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       ```

     

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       ## Part 1

     

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       ```elixir

     

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       1..25

     

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       |> Enum.reduce(stones, fn _, acc ->

     

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         Stones.blink(acc)

     

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       end)

     

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       |> Map.values()

     

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       |> Enum.sum()

     

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       ```

     

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       ```

     

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       209412

     

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       ```

     

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       ## Part 2

     

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       ```elixir

     

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       1..75

     

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       |> Enum.reduce(stones, fn _, acc ->

     

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         Stones.blink(acc)

     

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       end)

     

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       |> Map.values()

     

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       |> Enum.sum()

     

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       ```

     

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       ```

     

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       248967696501656

     

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       ```

     

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