Harshad (Niven) Number

/*
 * Problem : Check if a number is a Harshad number.
 * Input   : One integer.
 * Output  : true or false.
 * Approach: Divide the number by its digit sum.
 * Time    : O(d)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method receives a number and returns true if the number is a Harshad number.
    static boolean isHarshad(long number) {
        // Step 1: Only positive numbers are checked. This also avoids division by zero later.
        if (number < 1) {
            return false;
        }

        // Step 2: Add the digits. The sum starts at 0.
        long digitSum = 0;
        long remaining = number;
        while (remaining > 0) {
            // Step 2a: Take the last digit and add it. Example: 18 % 10 = 8.
            digitSum = digitSum + remaining % 10;

            // Step 2b: Remove the last digit. Example: 18 / 10 = 1.
            remaining = remaining / 10;
        }

        // Step 3: The number is a Harshad number if it divides by the digit sum without remainder.
        return number % digitSum == 0;
    }

    public static void main(String[] args) {
        long number = new Scanner(System.in).nextLong();
        System.out.println(isHarshad(number));
    }
}