LeetCode-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:

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

很简单的递归实现

class Solution {
public:
    void Sub(vector<string>* ret,string* s,int level,int left,int current){
        if(left==0){
            while(level>0){
                (*s)[current]=')';
                level--;
                current++;
            }
            (*ret).push_back(*s);
        }
        else{
            (*s)[current]='(';
            Sub(ret,s,level+1,left-1,current+1);
            if(level!=0){
                (*s)[current]=')';
                Sub(ret,s,level-1,left,current+1);
            }
        }
    }
    vector<string> generateParenthesis(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<string> ret;
        string s;
        s.resize(2*n);
        Sub(&ret,&s,0,n,0);
        return ret;
    }
};