Generate Parentheses

题目描述：

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: 

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

　　这题没做出来，惭愧。

solution：

void dfs(vector<string> &result,string str,int left,int right)
{
    if(left > right)
        return;
    if (left == 0 && right == 0)
    {
        result.push_back(str);
        return;
    }
    if(left > 0)
        dfs(result, str+"(", left-1, right);
    if(right > 0)
        dfs(result, str+")", left, right-1);
}

vector<string> generateParenthesis(int n) {
    vector<string> res;
    if(n < 1) 
        return res;
    dfs(res, "", n, n);
    return res;
}

原文链接：http://blog.csdn.net/linhuanmars/article/details/19873463