小白笔记----------------------------------leetcode(22. Generate Parentheses )

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

这道算法涉及到什么卡特兰数，我们把他考虑成一个树的剪枝问题，确定剪枝的条件，就是剩余的左括号树一定大于右括号数。

本文算法，采纳自这篇大牛博客，详细解释，请跳转http://blog.youkuaiyun.com/yutianzuijin/article/details/13161721

public class Solution {
    public List<String> generateParenthesis(int n) {
        String result = "";
        List<String> result1 = new LinkedList();//两个规则，一个是要对称，一个是全部情况
        result1 = backtrack(n,n,result,result1);
            
        
        return result1;
    }
    public List<String> backtrack(int leftnum,int rightnum,String s,List<String> result){
        if(leftnum == 0 && rightnum == 0){
            result.add(s);
        }
        if(leftnum > 0){
            backtrack(leftnum-1,rightnum,s.concat("("),result);
        }
        if(rightnum > 0 && leftnum < rightnum){
            backtrack(leftnum,rightnum-1,s.concat(")"),result);
        }
        return result;
    }
}