[LeetCode] 22. 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:

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

解法: backtracking + 递归, 直接套用backtracking的模板解法.

class Solution {
public:
    vector<string> generateParenthesis(int n) {
        vector<string> allsol;
        string sol;
        
        gp(n, 0, 0, sol, allsol);
        return allsol;
    }
    
    void gp(int n, int nleft, int nright, string& sol, vector<string>& allsol) {
       if (nleft == n && nright == n){
           allsol.push_back(sol);
           return;
       }
       
       if (nleft < n){
           sol.push_back('(');
           gp(n, nleft+1, nright,sol, allsol);
           sol.pop_back();
       }
       
       if (nleft > nright){
           sol.push_back(')');
           gp(n, nleft, nright+1, sol,allsol);
           sol.pop_back();
       }
       
       return;
    }
};