22. Generate Parentheses

22. Generate Parentheses

Pick One

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:

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

Seen this question in a real interview before? Yes

No
思路：递归法，两个限制条件：
1，左括号和右括号的数量都为0的时候
2，只有当左括号<右括号的数量时才能添加右括号上去，否则无效
AC代码：

class Solution {
public:
    vector<string> generateParenthesis(int n) {
        vector<string> result;
        generate("",n,n,result);
        return result;
    }
private:
    void generate(string item,int left,int right,vector<string> &result){
        if(left==0&&right==0){
            result.push_back(item);
            return;
        }
        if(left>0){
            generate(item+'(',left-1,right,result);
        }
        if(left<right){
            generate(item+')',left,right-1,result);
        }
    }
};