LongestValidParenthesisSubString.java

import java.util.*;
public class LongestValidParenthesisSubString {
      

    public int longestValidParentheses(String s) {

    Stack<Integer> stack = new Stack<>();
    int maxLength = 0;
    int lastInvalid = -1;

    for (int i = 0; i < s.length(); i++) {

        if (s.charAt(i) == '(') {
            stack.push(i);
        } else {
            if (stack.isEmpty()) {
                lastInvalid = i;
            } else {
                stack.pop();
                if (stack.isEmpty()) {
                    maxLength = Math.max(maxLength, i - lastInvalid);
                } else {
                    maxLength = Math.max(maxLength, i - stack.peek());
             }
          } 
       }
     }
    return maxLength;
}
    
    
    
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        System.out.println("Enter the parentheses to check!!");
        String str= sc.nextLine();
        LongestValidParenthesisSubString ob= new LongestValidParenthesisSubString();

        int res=ob.longestValidParentheses(str);

        System.out.println(res);

        
    }
}