【leetcode】Generate Parentheses

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:

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

 

 

用递归生成所有的括号组合，并且在递归过程中不断剪枝

剪枝的条件：

 leftNum>n||rightNum>n||rightNum>leftNum)

1.左、右括号数目大于了n

2.右括号数目大于了左括号数目

 

 

class Solution {

public:

    vector<string> generateParenthesis(int n) {

       

        vector<string> result;

        generate(result,"",0,n,0,0);

        return result;

       

    }

   

    void generate(vector<string> &result,string tmp,int index,int &n,int leftNum,int rightNum)

    {

        if(leftNum>n||rightNum>n||rightNum>leftNum)

        {

            return;

        }

        if(index==2*n)

        {

            result.push_back(tmp);

            return;

        }

       

        generate(result,tmp+"(",index+1,n,leftNum+1,rightNum);

        generate(result,tmp+")",index+1,n,leftNum,rightNum+1);

    }

};