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.
public class Solution {
public int longestValidParentheses(String s) {
int maxLen = 0;
Stack<Integer> stack = new Stack<Integer>();
int left = 0;
for(int i=0;i<s.length();i++)
{
if(s.charAt(i) == '(')
stack.push(i);
else
{
if(stack.empty())
left = i+1; //记录起始位置的下标
else
{
stack.pop();
if(stack.empty())
maxLen = Math.max(maxLen,i-left+1);
else
maxLen = Math.max(maxLen,i-stack.peek());
}
}
}
return maxLen;
}
}
