LeetCode: Valid Parentheses 解题报告

 1 public class Solution {
 2     public boolean isValid(String s) {
 3         if (s == null || s.length() == 0) {
 4             return true;
 5         }
 6         
 7         Stack<Character> stack = new Stack<Character>();
 8         int len = s.length();
 9         for (int i = 0; i < len; i++) {
10             char c = s.charAt(i);
11             if (stack.isEmpty()) {
12                 // 栈为空的时候，不能放右括号
13                 if (c == ‘]‘ || c == ‘)‘ || c == ‘}‘) {
14                     return false;
15                 }
16                 stack.push(c);
17                 continue;
18             }
19             
20             // 栈不为空时，必须 要对应弹出相对应的括号
21             if (c == ‘)‘ && stack.peek() == ‘(‘
22                || c == ‘]‘ && stack.peek() == ‘[‘
23                || c == ‘}‘ && stack.peek() == ‘{‘
24                ) {
25                 stack.pop();
26             // 或者继续压入左括号    
27             } else if (c == ‘(‘ || c == ‘[‘ || c == ‘{‘) {
28                 stack.push(c);
29             // 否则错误退出    
30             } else {
31                 return false;
32             }
33         }
34         
35         return stack.isEmpty();
36     }
37 }