Time Difference (HH:MM:SS)

/*
 * Problem : Time difference.
 * Input   : Two times.
 * Output  : The difference.
 * Approach: Seconds since midnight.
 * Time    : O(1)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Convert a time HH:MM:SS to the number of seconds since midnight.
        static long toSeconds(String time) {
            String[] part = time.split(":");
            return Long.parseLong(part[0]) * 3600 + Long.parseLong(part[1]) * 60 + Long.parseLong(part[2]);
        }

    // This method solves the task. It receives the input and returns the answer.
    static String solve(String a, String b) {
        // Step 1: Work with seconds since midnight. This turns time arithmetic into simple number arithmetic.
        long difference = toSeconds(b) - toSeconds(a);

        // Step 2: If the end is earlier, add one day. We also use the remainder, so equal times give 0.
        difference = ((difference % 86400) + 86400) % 86400;

        // Step 3: Convert the seconds back to hours, minutes and seconds with two digits each.
        return String.format("%02d:%02d:%02d", difference / 3600, difference % 3600 / 60, difference % 60);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String a = scanner.next();
        String b = scanner.next();
        System.out.println(solve(a, b));
    }
}