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:

"((()))", "(()())", "(())()", "()(())", "()()()"

 1 class Solution { 2  3 public: 4  5     vector<string> generateParenthesis(int n) { 6  7         8  9         vector<string> result;10 11         generate(result,"",0,n,0,0);12 13         return result;14 15        16 17     }18 19    20 21     void generate(vector<string> &result,string tmp,int index,int &n,int leftNum,int rightNum)22 23     {24 25         if(leftNum>n||rightNum>n||rightNum>leftNum)26 27         {28 29             return;30 31         }32 33         if(index==2*n)34 35         {36 37             result.push_back(tmp);38 39             return;40 41         }42 43        44 45         generate(result,tmp+"(",index+1,n,leftNum+1,rightNum);46 47         generate(result,tmp+")",index+1,n,leftNum,rightNum+1);48 49     }50 51 };