92 lines
2.1 KiB
Elixir
92 lines
2.1 KiB
Elixir
defmodule Day8 do
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defp read_input do
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Path.expand('input', Path.dirname(__ENV__.file))
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|> File.read!()
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end
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defp parse_program(text) do
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String.split(String.trim(text), "\n")
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|> Enum.map(fn line ->
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[op, val] = String.split(line)
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{op, String.to_integer(val)}
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end)
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end
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defp tick(program, pc, acc) do
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case Enum.at(program, pc) do
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{"nop", _} -> {pc + 1, acc}
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{"acc", int} -> {pc + 1, acc + int}
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{"jmp", int} -> {pc + int, acc}
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end
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end
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defp find_loop(program, pc, acc, history) do
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{next_pc, next_acc} = tick(program, pc, acc)
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count = Map.get(history, next_pc, 0)
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if count > 0 do
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acc
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else
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find_loop(program, next_pc, next_acc, Map.put(history, next_pc, count + 1))
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end
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end
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def part1 do
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program = parse_program(read_input())
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find_loop(program, 0, 0, %{})
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end
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def run(program, pc, acc, history, term_pc) do
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{next_pc, next_acc} = tick(program, pc, acc)
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count = Map.get(history, next_pc, 0)
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cond do
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count > 0 -> :loop
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next_pc == term_pc -> {:term, next_acc}
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next_pc > term_pc -> :wtf
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true -> run(program, next_pc, next_acc, Map.put(history, next_pc, count + 1), term_pc)
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end
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end
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def mod(program, ridx) do
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Enum.with_index(program)
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|> Enum.map(fn {{op, val}, idx} ->
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if idx == ridx do
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case op do
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"nop" -> {"jmp", val}
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"jmp" -> {"nop", val}
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_ -> {op, val}
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end
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else
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{op, val}
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end
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end)
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end
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def mods(program) do
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Stream.with_index(program)
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|> Stream.filter(fn {{op, _val}, _idx} ->
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case op do
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"acc" -> false
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"nop" -> true
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"jmp" -> true
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end
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end)
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|> Stream.map(fn {_, idx} -> mod(program, idx) end)
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end
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def part2 do
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program = parse_program(read_input())
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term_pc = Enum.count(program)
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Enum.reduce_while(mods(program), nil, fn modded_program, _ ->
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case run(modded_program, 0, 0, %{}, term_pc) do
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:loop -> {:cont, nil}
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{:term, acc} -> {:halt, acc}
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end
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end)
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end
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end
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Day8.part1() |> IO.inspect()
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Day8.part2() |> IO.inspect()
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