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day01: part 1
Preemptively create a *_part_1, because we all know how AOC puzzles go...
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lib/day01.ex
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lib/day01.ex
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defmodule Aoc2025.Day01 do
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@moduledoc false
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@day 1
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@example """
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L68
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L30
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R48
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L5
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R60
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L55
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L1
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L99
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R14
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L82
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"""
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def output_parsed_example, do: parse_input(@example)
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def output_parsed_input, do: parse_input(Aoc2025.Utils.get_input(@day))
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def parse_input(input), do: String.split(input)
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def parse_instruction("L" <> distance), do: {:left, String.to_integer(distance)}
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def parse_instruction("R" <> distance), do: {:right, String.to_integer(distance)}
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def inc_if_zero(acc, dial) when dial == 0, do: acc + 1
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def inc_if_zero(acc, _dial), do: acc
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def direction_to_op(:left), do: &Kernel.-/2
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def direction_to_op(:right), do: &Kernel.+/2
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def double_modulo_after_op(op, dial, distance), do: rem(rem(op.(dial, distance), 100) + 100, 100)
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def compute_part_1(input) do
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input
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|> Enum.map(&parse_instruction/1)
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|> Enum.reduce({0, 50}, fn {direction, distance}, {acc_ans, dial} ->
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new_dial =
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direction
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|> direction_to_op()
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|> double_modulo_after_op(dial, distance)
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{inc_if_zero(acc_ans, new_dial), new_dial}
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end)
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end
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end