53 lines
1.4 KiB
Elixir
53 lines
1.4 KiB
Elixir
defmodule Day8Part2 do
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def run do
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File.read!("input")
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|> input_to_instrs()
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|> find_corrupted()
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|> IO.puts()
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end
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def input_to_instrs(input) do
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input
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|> String.split("\n", trim: true)
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|> Enum.map(&String.split/1)
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|> Enum.with_index()
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|> Map.new(fn {[op, arg], idx} -> {idx, {op, String.to_integer(arg)}} end)
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end
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def find_corrupted(instrs), do: find_corrupted(Map.to_list(instrs), instrs, :loop)
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def find_corrupted(_rest, _instrs, {:terminated, acc}), do: acc
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def find_corrupted([{idx, {op, arg}} | rest], instrs, :loop) do
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result =
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instrs
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|> Map.put(idx, toggle_op(op, arg))
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|> try_boot()
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find_corrupted(rest, instrs, result)
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end
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def toggle_op("acc", arg), do: {"acc", arg}
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def toggle_op("nop", arg), do: {"jmp", arg}
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def toggle_op("jmp", arg), do: {"nop", arg}
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def try_boot(instrs), do: try_boot(instrs, 0, 0, MapSet.new())
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def try_boot(instrs, idx, acc, _seen) when idx == map_size(instrs), do: {:terminated, acc}
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def try_boot(instrs, idx, acc, seen) do
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if MapSet.member?(seen, idx) do
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:loop
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else
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seen = MapSet.put(seen, idx)
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{idx, acc} = execute(instrs[idx], idx, acc)
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try_boot(instrs, idx, acc, seen)
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end
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end
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def execute({"nop", _arg}, idx, acc), do: {idx + 1, acc}
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def execute({"jmp", arg}, idx, acc), do: {idx + arg, acc}
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def execute({"acc", arg}, idx, acc), do: {idx + 1, acc + arg}
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end
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Day8Part2.run()
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