Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

Example 1:
Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()"

Example 2:
Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()"

Solution：

思路：
http://www.cnblogs.com/grandyang/p/4424731.html

Time Complexity: O() Space Complexity: O()

Solution Code：