32 lines
778 B
Elixir
32 lines
778 B
Elixir
defmodule Day15 do
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@input [18, 8, 0, 5, 4, 1, 20]
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def run do
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[stop] = System.argv()
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start(@input, nil, 1, String.to_integer(stop), %{})
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|> IO.puts()
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end
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def start([], prev_num, round, stop, state), do: play(prev_num, round, stop, state)
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def start([num | rest], _prev_num, round, stop, state) do
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start(rest, num, round + 1, stop, Map.put(state, num, {round, round}))
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end
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def play(prev_num, stop, stop, state), do: next_num(prev_num, state)
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def play(prev_num, round, stop, state) do
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num = next_num(prev_num, state)
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state = Map.update(state, num, {round, round}, fn {_a, b} -> {b, round} end)
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play(num, round + 1, stop, state)
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end
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def next_num(prev_num, state) do
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{a, b} = state[prev_num]
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b - a
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end
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end
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Day15.run()
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