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.
1 public class Solution { 2 public int longestValidParentheses(String s) { 3 if (s == null) { 4 return 0; 5 } 6 int maxlen=0; 7 Stack<Integer> stack = new Stack<Integer>(); 8 stack.add(-1); 9 for (int i = 0; i < s.length(); i++) { 10 if (s.charAt(i) == ‘(‘) { 11 stack.add(i); 12 } else { 13 stack.pop(); 14 if (stack.isEmpty()) { 15 stack.add(i); 16 } else { 17 maxlen=Math.max(maxlen,i-stack.peek()); 18 } 19 } 20 } 21 return maxlen; 22 } 23 }
LeetCode Longest Valid Parentheses
原文：http://www.cnblogs.com/birdhack/p/4197801.html