82 lines
2.1 KiB
Elixir
82 lines
2.1 KiB
Elixir
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defmodule Day23Part2 do
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@input "137826495"
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def run do
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{a, b} =
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@input
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|> String.graphemes()
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|> Enum.map(&String.to_integer/1)
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|> init_cups()
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|> play(10_000_000)
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|> next_two_after_1()
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IO.puts("Next two cups: #{a}, #{b}")
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IO.puts("Answer: #{a * b}")
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end
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def init_cups([first, second | _] = input) do
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cups = :ets.new(:circle, [])
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(input ++ for(i <- 10..1_000_000, do: i))
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|> Stream.chunk_every(3, 1)
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|> Stream.each(fn
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[a, b, c] ->
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:ets.insert(cups, {b, {a, c}})
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[penultimate, last] ->
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:ets.insert(cups, {first, {last, second}})
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:ets.insert(cups, {last, {penultimate, first}})
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end)
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|> Stream.run()
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{first, cups}
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end
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def play({_current, cups}, 0), do: cups
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def play(state, times), do: move(state) |> play(times - 1)
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def move({current, cups}) do
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holding = take_three(cups, current)
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dest = find_dest(holding, current)
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cups = insert(holding, dest, cups)
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[{^current, {_prev, next}}] = :ets.lookup(cups, current)
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{next, cups}
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end
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def find_dest(holding, 1), do: find_dest(holding, 1_000_001)
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def find_dest(holding, current) do
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dest = current - 1
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if dest in holding, do: find_dest(holding, dest), else: dest
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end
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def take_three(cups, current) do
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[{^current, {prev, a}}] = :ets.lookup(cups, current)
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[{^a, {^current, b}}] = :ets.lookup(cups, a)
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[{^b, {^a, c}}] = :ets.lookup(cups, b)
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[{^c, {^b, next}}] = :ets.lookup(cups, c)
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[{^next, {^c, last}}] = :ets.lookup(cups, next)
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:ets.insert(cups, {current, {prev, next}})
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:ets.insert(cups, {next, {current, last}})
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[a, b, c]
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end
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def insert([a, b, c], dest, cups) do
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[{^dest, {prev, next}}] = :ets.lookup(cups, dest)
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[{^next, {^dest, last}}] = :ets.lookup(cups, next)
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:ets.insert(cups, {dest, {prev, a}})
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:ets.insert(cups, {a, {dest, b}})
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:ets.insert(cups, {c, {b, next}})
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:ets.insert(cups, {next, {c, last}})
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cups
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end
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def next_two_after_1(cups) do
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[{1, {_prev, next}}] = :ets.lookup(cups, 1)
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[{^next, {1, nextnext}}] = :ets.lookup(cups, next)
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{next, nextnext}
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end
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end
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Day23Part2.run()
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