[leetcode]22. Generate Parentheses

题目链接：https://leetcode.com/problems/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:

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

class Solution{
public:
    vector<string> generateParenthesis(int n)
    {
        vector<string> result;
        combination(result,"",n,n);
        return result;
    }

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