Leetcode-Python/0022.py at master · mscully4/Leetcode-Python · GitHub

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class Solution:
    def generateParenthesis(self, n: int) -> List[str]:
        memory = {
            "(": n,
            ")": n
        }

        answers = set()

        def recurse(string, memory, answers):
            # print(string, memory)
            if len(string) == n * 2:
                if self.is_valid(string):
                    answers.add(string)

            elif len(string) < n * 2:
                left_counter = memory["("]

                if left_counter > 0:
                    recurse(string + "(", {"(": memory["("] - 1, ")": memory[")"]}, answers)

                right_counter = memory[")"]
                if right_counter > 0:
                    recurse(string + ")", {")": memory[")"] - 1, "(": memory["("]}, answers)

        recurse("", memory, answers)
        return answers

    def is_valid(self, string):
        if len(string) % 2 != 0:
            return False

        stack = []

        for i in range(len(string)):
            if string[i] == "(":
                stack.append(string[i])
            else:
                if not stack:
                    return False
                elif stack.pop() != "(":
                    return False

        return True if not stack else False