LongestValidParentheses, 求最长合法括号子串长度-----同类问题ValidParentheses，GenerateParentheses

 1 public static int longestValidParentheses(String s) {
 2         Stack<int[]> stack = new Stack<int[]>();
 3         int result = 0;
 4      
 5         for(int i=0; i<=s.length()-1; i++)
 6         {
 7             char c = s.charAt(i);
 8             if(c==‘(‘)//如果是左括号
 9             {
10                 int[] a = {i,0};
11                 stack.push(a);
12             }
13             else//如果是右括号
14             {
15                 if(stack.empty()||stack.peek()[1]==1)//如果栈为空或者栈顶元素为右括号
16                 {
17                     int[] a = {i,1};
18                     stack.push(a);
19                 }
20                 else
21                 {
22                     stack.pop();
23                     int currentLen=0;
24                     if(stack.empty())
25                     {
26                         currentLen = i+1;
27                     }
28                     else
29                     {
30                         currentLen = i-stack.peek()[0];
31                     }
32                     result = Math.max(result, currentLen);
33                 }
34             }
35         }
36      
37         return result;
38     }