GCD of Two Numbers

/*
 * Problem : Find the greatest common divisor (GCD) of two numbers.
 * Input   : Two non-negative integers on one line.
 * Output  : Their GCD.
 * Approach: Use the Euclidean algorithm: replace (a, b) by (b, a % b).
 * Time    : O(log(min(a, b)))
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long first = scanner.nextLong();
        long second = scanner.nextLong();

        // Step 1: Repeat until the second number is 0.
        while (second != 0) {
            // Step 2: The GCD of (a, b) is the same as the GCD of (b, a % b). Example: gcd(48, 36) = gcd(36, 12).
            long remainder = first % second;
            first = second;
            second = remainder;
        }

        // Step 3: When the second number is 0, the first number is the GCD. Example: gcd(12, 0) = 12.
        System.out.println(first);
    }
}