Java Exercises: Check whether a given number is a happy number or unhappy number

Java Numbers: Exercise-10 with Solution

Write a Java program to check whether a given number is a happy number or unhappy number.

Happy number: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1, or it loops endlessly in a cycle which does not include 1.
An unhappy number is a number that is not happy.
The first few unhappy numbers are 2, 3, 4, 5, 6, 8, 9, 11, 12, 14, 15, 16, 17, 18, 20.

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Example10 {

    public static boolean isHappy_number(int num)
    {
        Set<Integer> unique_num = new HashSet<Integer>();

        while (unique_num.add(num))
        {
            int value = 0;
            while (num > 0)
            {
                value += Math.pow(num % 10, 2);
                num /= 10;
            }
            num = value;
        }

        return num == 1;
    }

    public static void main(String[] args)
    {
        System.out.print("Input a number: ");
        int num = new Scanner(System.in).nextInt();
        System.out.println(isHappy_number(num) ? "Happy Number" : "Unhappy Number");
    }
}

Sample Output:

Input a number: 5                                                                                             
Unhappy Number

Flowchart:

Java Code Editor:

Contribute your code and comments through Disqus.

Previous: Write a Java program to find and print the first 10 happy numbers.
Next: Write a Java program to check whether a given number is a Disarium number or unhappy number.