43 lines
1 KiB
Elixir
43 lines
1 KiB
Elixir
defmodule Day13Part2 do
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def run do
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schedule =
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File.read!("input")
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|> String.split(["\n", ","], trim: true)
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|> Enum.drop(1)
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|> Enum.map(&parse_schedule/1)
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|> Enum.with_index()
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|> Enum.reject(&match?({:any, _}, &1))
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|> IO.inspect()
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{max_id, max_offset} =
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Enum.max(schedule, fn {id1, _}, {id2, _} -> id1 >= id2 end)
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|> IO.inspect()
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start_time =
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Enum.reduce(schedule, 1, fn {id, _}, acc -> id * acc end)
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|> Kernel.-(max_offset)
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|> IO.inspect(label: "start time")
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find_sequential_departures(start_time, schedule, max_id)
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|> IO.inspect()
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end
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def parse_schedule(id) do
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case Integer.parse(id) do
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{id, ""} -> id
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_ -> :any
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end
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end
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def find_sequential_departures(t, busses, period) do
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if Enum.all?(busses, fn {id, offset} -> departs_at_offset?(t, id, offset) end) do
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t
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else
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find_sequential_departures(t - period, busses, period)
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end
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end
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def departs_at_offset?(t, id, offset), do: rem(t + offset, id) == 0
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end
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Day13Part2.run()
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