Generate Parentheses

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:

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

 

Analyse: As long as number of "(" is smaller than n, we can push "(", as long as number of ")" is smaller than "(", we can push ")". 

Runtime: 0ms.

 1 class Solution {
 2 public:
 3     vector<string> generateParenthesis(int n) {
 4         vector<string> result;
 5         if(!n) return result;
 6         
 7         helper(n, 0, 0, result, "");
 8         return result;
 9     }
10     
11     void helper(int n, int left, int right, vector<string>& result, string temp) {
12         if(left == n && right == n) {
13             result.push_back(temp);
14             return;
15         }
16         if(left < n) helper(n, left + 1, right, result, temp + "(");
17         if(right < left && right < n) helper(n, left, right + 1, result, temp + ")");
18     }
19 };

 

posted @ 2016-08-09 23:19  amazingzoe  阅读(103)  评论(0)  编辑  收藏  举报