题解 | #最长的括号子串#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return int整型
     */
    public int longestValidParentheses (String s) {
        // write code here
        int res = 0;
        int start = -1;
        Stack<Integer> st = new Stack<>();
        for(int i = 0; i < s.length();i++){
            if(s.charAt(i) == '('){
                st.push(i);
            }else{
                if(st.isEmpty()){
                    start = i;
                }else{
                    st.pop();
                    if(!st.isEmpty()){
                        res = Math.max(res,i - st.peek());
                    }else{
                        res = Math.max(res,i - start);
                    }
                }
            }
        }
         return res;
    }
}