AdventOfCode/2020/elixir/day23/day23part1.exs

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Elixir
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2020-12-25 08:57:30 +00:00
defmodule Day23Part1 do
# @input "389125467"
@input "137826495"
def run do
@input
|> String.graphemes()
|> Enum.map(&String.to_integer/1)
|> play(100)
|> cycle_to(1)
|> Enum.drop(1)
|> Enum.join()
|> IO.puts()
end
def play(cups, 0), do: cups
def play(cups, times), do: move(cups) |> play(times - 1)
def move([current, a, b, c | rest]) do
holding = [a, b, c]
dest = find_dest(current, holding)
insert(holding, dest, [current | rest])
|> cycle_to(current, 1)
end
def find_dest(1, holding), do: find_dest(10, holding)
def find_dest(current, holding) do
dest = current - 1
if dest in holding, do: find_dest(dest, holding), else: dest
end
def insert(holding, dest, circle) do
[dest | rest] = cycle_to(circle, dest)
[dest | holding] ++ rest
end
def cycle_to(circle, target, offset \\ 0) do
circle
|> Stream.cycle()
|> Stream.drop_while(&(&1 != target))
|> Stream.take(length(circle) + offset)
|> Enum.drop(offset)
end
end
Day23Part1.run()