Leetcode 22. Generate Parentheses

发布时间：2020-12-14 05:11:15 所属栏目：大数据来源：网络整理

导读：https://leetcode.com/problems/generate-parentheses/ Medium Given? n ?pairs of parentheses,write a function to generate all combinations of well-formed parentheses. For example,given? n ?= 3,a solution set is: [ "((()))","(()())","(())()","

https://leetcode.com/problems/generate-parentheses/

Medium

Given?n?pairs of parentheses,write a function to generate all combinations of well-formed parentheses.

For example,given?n?= 3,a solution set is:

[
  "((()))","(()())","(())()","()(())","()()()"
]

回溯，DFS。学习判断括号有效的剪枝技巧。
https://leetcode.com/problems/generate-parentheses/solution/

 1 class Solution:
 2     def generateParenthesis(self,n: int) -> List[str]:
 3         if n == 0:
 4             return None
 5         
 6         result = []
 7         
 8         def helper(s = ‘‘,left = 0,right = 0):
 9             if len(s) == 2 * n:
10                 result.append(s)
11                 return
12             
13             if left < n:
14                 helper(s + ‘(‘,left + 1,right)
15             
16             if right < left:
17                 helper(s + ‘)‘,left,right + 1)
18         
19         helper()
20         return result

View Python Code

（编辑：李大同）

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