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defmodule Three do
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def max_combination(list, k) do
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map =
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list
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|> Enum.with_index()
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|> Enum.map(fn {item, index} -> {index, item - ?0} end)
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|> Enum.into(%{})
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length = length(list)
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combinations_from(map, length, k, 0, 0, 0, [], [], 0)
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end
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def combinations_from(map, length, k, acc, index, con, [lastix | ixsub], [_ | sub], sublen)
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when index == length and lastix + 1 == length,
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do: combinations_from(map, length, k, acc, length, div(con, 10), ixsub, sub, sublen - 1)
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def combinations_from(map, length, k, acc, index, con, [lastix | ixsub], [_ | sub], sublen)
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when index == length,
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do: combinations_from(map, length, k, acc, lastix + 1, div(con, 10), ixsub, sub, sublen - 1)
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def combinations_from(_map, length, _k, acc, index, _con, _ixsub, _sub, _sublen) when index == length,
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do: acc
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def combinations_from(map, length, k, acc, index, con, ixsub, sub, sublen) do
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cond do
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sublen == k - 1 ->
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acc = max(acc, con*10 + map[index])
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combinations_from(map, length, k, acc, index + 1, con, ixsub, sub, sublen)
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(con * 10 + map[index] + 1) * (10 ** (k - sublen - 1)) >= acc ->
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combinations_from(map, length, k, acc, index + 1, con * 10 + map[index], [index | ixsub], [map[index] | sub], sublen + 1)
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true ->
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combinations_from(map, length, k, acc, index + 1, con, ixsub, sub, sublen)
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end
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end
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end
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# input = """
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# 987654321111111
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# 811111111111119
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# 234234234234278
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# 818181911112111
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# """
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input = File.read!("3.input")
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input
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|> String.trim()
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|> String.split("\n")
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|> Task.async_stream(fn bank ->
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bank
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|> String.to_charlist()
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|> Three.max_combination(12)
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|> IO.inspect()
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end, timeout: :infinity, max_concurrency: 8)
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|> Enum.sum_by(fn {:ok, n} -> n end)
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|> IO.inspect
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