Leetcode 32 - study Java code of Leetcode 32 - longest valid parentheses - Hard level algorithm - code is from blog: http://blog.csdn.net/worldwindjp/article/details/39460161

Leetcode32_studyCode.java

public class Solution {  
    public int longestValidParentheses(String s) {  
        if(s == null || s.length() == 0) {  
            return 0;  
        }  
      
        int start     = -1;  
        int maxLength = 0;  
      
        Stack stack   = new Stack();  
      
        for(int i = 0;i < s.length(); i++) {  
            if(s.charAt(i) == '(') {  
                stack.push(i);  
            } else {  
                if(!stack.empty()) {  
                    stack.pop();  
                    if(stack.empty() == true) {  
                        maxLength = Math.max(i - start , maxLength);  
                    } else {  
                        maxLength = Math.max(i - (int)stack.peek() , maxLength);  
                    }  
                } else {  
                    start = i;  
                }  
            }  
        }  
      
        return maxLength;  
    }  
}