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2024 day 11
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2024/day11.livemd
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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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<!-- livebook:{"output":true} -->
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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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<!-- livebook:{"output":true} -->
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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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<!-- livebook:{"output":true} -->
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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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<!-- livebook:{"output":true} -->
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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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<!-- livebook:{"output":true} -->
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```
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248967696501656
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```
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<!-- livebook:{"offset":1963,"stamp":{"token":"XCP.YCGtDQl3XNWJm5oY1OPI2QDRB7EIjZxBmwK3eswS1ryD28kg8fS_fKGIFJGFbtL1NL7wYrv2ADW60yeAZnCv5KbDelUm_bxkPN4_K56iTJ1toOGfIRYlo2lj5beAjrmbhRw","version":2}} -->