Generate Parentheses

递归。传入的前两个参数分别表示未分配的左括号数和未匹配的左括号数。

 1     void fill(int numOfRemain, int numToMatch, string tmp, vector<string> &result){
 2         if(numOfRemain == 0 && numToMatch == 0){
 3             result.push_back(tmp);
 4             return;
 5         }
 6         if(numOfRemain > 0){
 7             tmp += '(';
 8             fill(numOfRemain-1, numToMatch+1, tmp, result);
 9             tmp.erase(tmp.length()-1);
10         }
11         if(numToMatch > 0){
12             tmp += ')';
13             fill(numOfRemain, numToMatch-1, tmp, result);
14              tmp.erase(tmp.length()-1);
15       }
16     }
17     vector<string> generateParenthesis(int n) {
18         // Start typing your C/C++ solution below
19         // DO NOT write int main() function
20         string tmp;
21         vector<string> vec;
22         fill(n,0,tmp,vec);
23         return vec;
24     }