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

Last update on March 11 2025 11:10:46 (UTC/GMT +8 hours)

Check Happy or Unhappy Number

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:

For more Practice: Solve these Related Problems:

• Write a Java program to check if a number is happy by using a HashSet to detect cycles.
• Write a Java program to recursively compute the happiness sequence of a number and return a boolean result.
• Write a Java program to implement and compare iterative and recursive methods for checking happy numbers.
• Write a Java program to print the intermediate sums in the happy number process and decide if a number is happy.

Java Code Editor:

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