leetcode--Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

 

 1 public class Solution {
 2     public boolean isValid(String s) {
 3        boolean isValid = true;
 4         if(s.length() > 0){
 5             Stack<Character> parenStack = new Stack<Character>();
 6             for(int i = 0; i <s.length(); ++i){
 7                 if(s.charAt(i) == '(' || s.charAt(i) == '[' || s.charAt(i) == '{')
 8                     parenStack.push(s.charAt(i));
 9                 else{
10                     if(s.charAt(i) == ')'){
11                         if(parenStack.empty() || parenStack.peek() != '(')
12                             isValid = false;
13                         else
14                             parenStack.pop();
15                     }
16                     if(s.charAt(i) == ']'){
17                         if(parenStack.empty() || parenStack.peek() != '[')
18                             isValid = false;
19                         else
20                             parenStack.pop();
21                     }
22                     if(s.charAt(i) == '}'){
23                         if(parenStack.empty() || parenStack.peek() != '{')
24                             isValid = false;
25                         else
26                             parenStack.pop();
27                     }                    
28                 }
29             }
30             if(! parenStack.empty())
31                 isValid = false;
32         }
33         return isValid;
34     }
35 }

 

posted @ 2014-01-31 01:09  Averill Zheng  阅读(162)  评论(0)  编辑  收藏  举报