49 lines
961 B
Elixir
49 lines
961 B
Elixir
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defmodule AOC.Day10 do
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def find_diffs(xs), do: find_diffs(xs, %{})
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def find_diffs([_], acc), do: acc
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def find_diffs([x1, x2 | xs], acc) do
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acc = Map.update(acc, x2 - x1, 1, &(&1 + 1))
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find_diffs([x2 | xs], acc)
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end
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def count_walks([x | _] = xs) do
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memo =
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Enum.into(xs, %{}, &{&1, 0})
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|> Map.put(x, 1)
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count_walks(xs, memo)
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end
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def count_walks([x], memo), do: memo[x]
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def count_walks([x | xs], memo) do
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memo =
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Enum.take(xs, 3)
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|> Enum.reduce(memo, fn
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next, memo when next - x <= 3 ->
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Map.update!(memo, next, &(&1 + memo[x]))
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_, memo ->
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memo
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end)
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count_walks(xs, memo)
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end
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def parts do
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input =
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AOC.Util.input_integers(10, 1)
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|> Enum.sort()
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input = [0 | input] ++ [Enum.max(input) + 3]
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%{1 => ones, 3 => threes} = find_diffs(input)
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part1 = ones * threes
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part2 = count_walks(input)
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{part1, part2}
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end
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end
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