leetcode32.最长有效括号（栈）

 1 class Solution{
 2 public int longestValidParentheses(String s ){
 3 LinkedList<Integer> stack = new LinkedList<Integer>();
 4 int res = 0;
 5 for(int i = 0; i < s.length();i++){
 6 if(stack.isEmpty() || s.chatAt(i) == "(" || s.chatAt(stack.getLast()) ==")"){
 7 stack.addLast(i);
 8 }else{
 9 srack.removeLast();
10 res = Math.max(res,stack.isEmpty ?  i + 1 : i - stack.getLast());
11 }
12 }
13 return res;
14 }
15 }