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[LeetCode] 22. Generate Parentheses

2016-10-01 22:28  amadis  阅读(121)  评论(0)  编辑  收藏  举报

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:

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

解法: backtracking + 递归, 直接套用backtracking的模板解法.
 1 class Solution {
 2 public:
 3     vector<string> generateParenthesis(int n) {
 4         vector<string> allsol;
 5         string sol;
 6         
 7         gp(n, 0, 0, sol, allsol);
 8         return allsol;
 9     }
10     
11     void gp(int n, int nleft, int nright, string& sol, vector<string>& allsol) {
12        if (nleft == n && nright == n){
13            allsol.push_back(sol);
14            return;
15        }
16        
17        if (nleft < n){
18            sol.push_back('(');
19            gp(n, nleft+1, nright,sol, allsol);
20            sol.pop_back();
21        }
22        
23        if (nleft > nright){
24            sol.push_back(')');
25            gp(n, nleft, nright+1, sol,allsol);
26            sol.pop_back();
27        }
28        
29        return;
30     }
31 };