1244B-Rooms and Staircases.java

package codeforces;

import java.util.Scanner;

public class roomsstaircases {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int t = scanner.nextInt();  // Number of test cases
        while (t-- > 0) {
            int n = scanner.nextInt();  // Number of rooms on each floor
            String s = scanner.next();  // String representing staircases

            // If there are no staircases, the maximum rooms Nikolay can visit is just the rooms on one floor
            if (!s.contains("1")) {
                System.out.println(n);
                continue;
            }

            // Find the first and last occurrences of '1'
            int firstStaircase = s.indexOf('1');
            int lastStaircase = s.lastIndexOf('1');

            // The maximum rooms Nikolay can visit is determined by the farthest stretch that includes both floors
            // He can visit rooms from the first to the last staircase, and both floors in that segment.
            int maxRooms = Math.max(lastStaircase + 1, n - firstStaircase) * 2;
            System.out.println(maxRooms);
        }
    }
}