39 lines
1.1 KiB
Elixir
39 lines
1.1 KiB
Elixir
defmodule AdventOfCode.Year2025.Dial do
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# Initial conditions
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def rotate(operations), do: rotate(50, operations, 0)
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# When no operations remain, return the number of zeroes
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def rotate(index, [], zeroes), do: { index, zeroes }
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# Compute the new dial position
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def rotate(index, [head | tail], zeroes) do
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{ new_index, _crosses } = case head do
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"R" <> number -> rotate_right(index, String.to_integer(number))
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"L" <> number -> rotate_left(index, String.to_integer(number))
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end
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case new_index do
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0 -> rotate(new_index, tail, zeroes+1)
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_ -> rotate(new_index, tail, zeroes)
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end
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end
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defp rotate_right(index, number) do
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crosses = div(number, 100)
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diff = index + rem(number, 100)
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case diff do
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diff when diff <= 99 -> { diff, crosses }
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diff when diff > 99 -> { diff - 100, crosses + 1 }
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end
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end
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defp rotate_left(index, number) do
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crosses = div(number, 100)
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diff = index - rem(number, 100)
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case diff do
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diff when diff >= 0 -> { diff, crosses }
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diff when diff < 0 -> { diff + 100, crosses + 1 }
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end
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end
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end
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