Given a string containing just the characters ‘(‘ and ‘)‘, find the length of the longest valid (well-formed) parentheses substring.
For "(()", the longest valid parentheses substring is "()", which has length = 2.
Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.
解题思路：
本题方法多多，是Java for LeetCode 020 Valid Parentheses题目的延续，因此，我们继续用栈的思路解决这个问题，其中需要一个index来维护最后一个‘)‘出现的位置。JAVA代码如下：
static public int longestValidParentheses(String s) {
int maxLength = 0,index=-1;
Stack<Integer> stack = new Stack<Integer>();
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == ‘(‘)
stack.push(i);
else {
if(stack.empty())
index=i;
else{
stack.pop();
if(stack.isEmpty())
maxLength = Math.max(maxLength, i - index);
else maxLength=Math.max(maxLength, i - stack.peek());
}
}
}
return maxLength;
}
Java for LeetCode 032 Longest Valid Parentheses
原文：http://www.cnblogs.com/tonyluis/p/4485849.html