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defmodule Ch1 do
@spec longest_parenthesis(s :: String.t()) :: integer
def longest_parenthesis(s) do
s
|> String.graphemes()
|> dp([], 0)
end
defp dp([], _, result), do: result
defp dp(["(" | tail], stack, result) do
dp(tail, [0 | stack], result)
end
defp dp([")" | tail], stack, result) do
{new_stack, new_result} = pop_until(stack, [])
dp(tail, new_stack, max(result, new_result))
end
defp pop_until([], _), do: {[], 0}
defp pop_until([0 | tail], rest) do
n = List.first(tail)
n = if n, do: n, else: 0
tail = if n > 0, do: tl(tail), else: tail
result = Enum.sum(rest) + n + 2
{[result | tail], result}
end
defp pop_until([h | tail], rest) do
pop_until(tail, [h | rest])
end
end
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