Java Exercises: Find and print the first 10 happy numbers

Java Numbers: Exercise-9 with Solution

Write a Java program to find and print the first 10 happy numbers.

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.

Example: 19 is a happy number
1² + 9²=82
8² + 2²=68
6² + 8²=100
1² + 0² + 0²=1

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.HashSet;
public class Example9 {
public static void main(String[] args){
	System.out.println("First 10 Happy numbers:");
       for(long num = 1,count = 0;count<8;num++){
           if(happy_num(num)){
               System.out.println(num);
               count++;
           }
       }
}
   public static boolean happy_num(long num){
       long m = 0;
       int digit = 0;
       HashSet<Long> cycle = new HashSet<Long>();
	   while(num != 1 && cycle.add(num)){
           m = 0;
           while(num > 0){
               digit = (int)(num % 10);
               m += digit*digit;
               num /= 10;
           }
           num = m;
       }
       return num == 1;
   }   
 }

Sample Output:

First 10 Happy numbers:                                                                                       
1                                                                                                  
7                                                                                                  
10                                                                                                  
13                                                                                                  
19                                                                                                  
23                                                                                                  
28                                                                                                  
31

Flowchart:

Java Code Editor:

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