22. 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:

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

本题开始做的时候以为用栈比较好,但是做错了,后来看了discussion 发现答案解法很好。用了两个open,close来做为假想的栈,代码如下:
 1 public class Solution {
 2     public List<String> generateParenthesis(int n) {
 3         List<String> res = new ArrayList<String>();
 4         backtracking(res,"",0,0,n);
 5         return res;
 6     }
 7     public void backtracking(List<String> res,String word,int open,int close,int max){
 8         if(word.length()==max*2){
 9             res.add(word);
10             return ;
11         }else{
12             if(open<max){
13                 backtracking(res,word+"(",open+1,close,max);
14             }
15             if(close<open){
16                 backtracking(res,word+")",open,close+1,max);
17             }
18         }
19     }
20 }

 

posted @ 2017-02-15 13:25  CodesKiller  阅读(114)  评论(0编辑  收藏  举报