75 lines
1.5 KiB
Elixir
75 lines
1.5 KiB
Elixir
import AOC
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import AOCHelpers
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aoc 2023, 8 do
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def p1(input) do
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{instructions, mappings} = read_input(input)
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all_but_last_step =
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instructions
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|> Stream.cycle()
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|> Stream.scan("AAA", &step(&1, &2, mappings))
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|> Stream.take_while(&(&1 != "ZZZ"))
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|> Enum.count()
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all_but_last_step + 1
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end
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def p2(input) do
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{instructions, mappings} = read_input(input)
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starts =
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mappings
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|> Map.keys()
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|> Enum.filter(&String.ends_with?(&1, "A"))
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lengths =
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starts
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|> Enum.map(fn start ->
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n =
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instructions
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|> Stream.cycle()
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|> Stream.scan(start, &step(&1, &2, mappings))
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|> Stream.take_while(&(not String.ends_with?(&1, "Z")))
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|> Enum.count()
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n + 1
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end)
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Enum.reduce(lengths, fn a, b ->
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div(a * b, Integer.gcd(a, b))
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end)
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end
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def step("L", curr, mappings) do
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mappings
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|> Map.get(curr)
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|> elem(0)
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end
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def step("R", curr, mappings) do
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mappings
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|> Map.get(curr)
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|> elem(1)
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end
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def step_all(inst, currs, mappings) do
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Enum.map(currs, &step(inst, &1, mappings))
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end
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def read_input(input) do
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[instructions_string, _ | mapping_lines] = lines(input)
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instructions = letters(instructions_string)
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mappings =
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mapping_lines
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|> Enum.map(fn mapping_line ->
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[_, key, left, right] = Regex.run(~r/^(.+) = \((.+), (.+)\)$/, mapping_line)
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{key, {left, right}}
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end)
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|> Enum.into(%{})
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{instructions, mappings}
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end
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end
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