LeetCode题库22.括号生成

 

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class Solution:     def generateParenthesis(self, n: int) -> List[str]:         if n==1:             return ['()']         if not n:             return None         stack,res,l,r=[],[],[],[]         for _ in range(n):             l.append('(')             r.append(')')         def dfs(l,r):             if not l and not r:                 res.append(''.join(i for i in stack))                 return             if l:                 stack.append(l.pop())                 dfs(l,r)                                l.append(stack.pop())                        if r and len(l)!=len(r):                 stack.append(r.pop())                 dfs(l,r)                 r.append(stack.pop())             print(r)         dfs(l,r)         return res