Question

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

Answer 1

Happy Numbers

Happy numbers are special numbers with a special property. We define a process as follows:

• Take a number N
• Replace the number N by the sum of squares of its digits
• Keep repeating the process until either it equals 1 or it runs into an infinite loop never equalling 1

If the process ends with 1, then the original number N is called a Happy Number.

Let us take an example:

-> N = 7

$7^2 = 49 \\ \\ 4^2+9^2 = 97 \\ \\ 9^2+7^2=130 \\ \\ 1^2+3^2+0^2=10 \\ \\ 1^2+0^2=1$

Thus, 7 is a Happy Number.

-> N = 8

$8^2 = 64 \\ \\ 6^2+4^2=52 \\ \\ 5^2+2^2=29 \\ \\ 2^2+9^2=85 \\ \\ \bold{8^2+5^2=89} \\ \\ 8^2+9^2=145 \\ \\ 1^2+4^2+5^2=42 \\ \\ 4^2+2^2=20 \\ \\ 2^2+0^2=4 \\ \\ 4^2 = 16 \\ \\ 1^2+6^2 = 37 \\ \\ 3^2+7^2=58 \\ \\ \bold{5^2+8^2=89}$

Note that we encountered 89 again. Both steps are highlighted in bold. We see that we are going to run into an infinite loop.

So, 8 is not a Happy Number.

So, if we are to write a program, what conditions do we keep so as to recognize when we are going into an infinite loop?

There can be many logics. The one I am going to show uses a special property of non-happy Numbers:

All non-happy numbers reach the cycle: 4, 16, 37, 58, 89, 145, 42, 20, 4, ...

So we can design a code, as follows:

/* A happy number is defined as follows:

* Start with any positive integer, replace the number by the sum of the squares of its digits,

* and repeat the process until the number either equals 1 (where it will stay),

* or it loops endlessly in a cycle which does not include 1.

*/

import java.util.*;

class HappyNumber {

   public static void main (String[] args) {

       Scanner sc = new Scanner(System.in);

       System.out.print("Enter a number: ");

       int N=sc.nextInt();         //Taking User Input

       if(N>0){

           boolean isHappy=false;      //Setting isHappy to false

           int s=sq(N);        //Taking s as sum of squares of digits of N

           while(s!=4){        //If s equals 4 at any point, then N is not a Happy Number

               if(s==1){      

                   isHappy=true;

                   break;

               }

               s=sq(s);        //Taking sum of squares of digits again

           }

           if(isHappy){

               System.out.println(N+" is a Happy Number.");

           }

           else{

               System.out.println(N+" is not a Happy Number.");

           }

       }

       else        //Program can only run for inputs of Natural Numbers. So invalid input case added.

       {

           System.out.println("Invalid input. Please enter only natural numbers.");

       }

   }

   static int sq(int n){       //Function to calculate sum of squares of digits of a number n

       int s=0;        //s will contain the answer

       while(n!=0){

           int d=n%10;     //Extracting each digit

           s+=d*d;         //Adding the square of the digit to s

           n=n/10;         //Reducing value of n by taking quotient of division by 10

       }

       return s;          

   }

}

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");

       }

   }

}