32.Longest Valid Parentheses

https://leetcode.com/problems/longest-valid-parentheses/solution/

1-Stack On

注意-1的使用

class Solution {
    public int longestValidParentheses(String s) {
        int maxLength = 0;
        Deque<Integer> stack = new ArrayDeque<>();
        stack.push(-1);
        for(int i = 0 ; i < s.length(); i++){
            if(s.charAt(i) == '('){
                stack.push(i);
            }
            else{
                stack.pop();
                if(stack.isEmpty()){
                    stack.push(i);
                }
                else{
                    maxLength = Math.max(maxLength, i - stack.peek());
                }
            }
        }
        return maxLength;
    }
}