LeetCode 022 Generate Parentheses

题目描述：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:

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

分析：

递归

代码如下：

class Solution {
private:
    vector<string> ret;
public:
    void solve(int dep, int maxDep, int leftNum, int leftNumTotal, string s)
    {
        //如果(个数超出，return
        if (leftNumTotal * 2 > maxDep)
            return;

        //如果长度足够，return
        if (dep == maxDep){
            ret.push_back(s);
            return;
        }

        for(int i = 0; i < 2; i++)

            //加 (
            if (i == 0)
                solve(dep + 1, maxDep, leftNum + 1, leftNumTotal + 1, s + ‘(‘);
            //加 )
            else if (leftNum > 0)
                solve(dep + 1, maxDep, leftNum - 1, leftNumTotal, s + ‘)‘);
    }

    vector<string> generateParenthesis(int n){
        ret.clear();
        solve(0, 2 * n, 0, 0, "");
        return ret;
    }
};