Question

write a program in java to check whether a number is a happy number or not

Answer 1

A number whose sum of the square of digits is ultimatly equal to 1 is a happy number. By ultimately we mean that starting with any positive number we continue the addition of square of digits till we get a single digit number (0 ~ 9). But the on whose sum is ultimately 1 is a happy number.

Example #1: 13 ; 12 + 32 = 1 + 9 =10 ; 12+ 02= 1 (Thus a happy number)
Example #2: 32; 3 2 + 2 2 = 9 + 4 = 13; and in Example#1 13 is already a happy number;
Some of the first happy numbers are: 1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82, 86, 91, 94, 97, 100, 103, 109, 129, 130.
Also See: java program for pattern with indentation
Java program to check for a happy number
import java.io.*;
class happynumber
{
public static void main(String args[])throws Exception
{
int i,j;
happyno obj=new happyno();
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("enter a number : ");
i=Integer.parseInt(br.readLine());
while((j=obj.happy(i))/10!=0) // You have to check the sum of all digits until a single digit is achieved i.e. sum=1,2,3,..9
{
i=j; // If sum of digits= 19 it then again goes to 1+9 =10 and again 1+0= '1' a single digit to check if 1 or not
}
if ( j==1)
System.out.println("It is a happy number ");
else
System.out.println("Not a happy number");
}

int happy(int n)
{
if(n/10==0)
return n*n;
else
return (int)Math.pow(n%10,2)+ happy(n/10);
}
}

Answer 2

import java.util.*;

class happy_number

{

   public static void main(String args[])

   {

       Scanner sc=new Scanner(System.in);

       System.out.println("Enter a number to check whether it is happy number or not");

       int n=sc.nextInt();

       int s=n;

       int d=0;

       while(s>9)

       {

           n=s;

           s=0;

           while(n>0)

           {

               d=n%10;

               s=s+(d*d);

               n=n/10;

           }

       }

       if(s==1)

       {

           System.out.println("Happy number");

       }

       else

       {

           System.out.println("Not a happy number");

       }

   }

}