# How to find Happy Number in JAVA

January 07, 2012## What is Happy Number

Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers .

Example: 19 is a happy number as

Likewise 1, 7, 10, 13, 19, 23 are happy numbers.

Source of photo and logic-http://www.transum.org/software/sw/starter_of_the_day/starter_January25.asp

## Logic

1. First we need to take two numbers as input: they are actually the ranges between which the Happy Numbers are to be found out.The first 'for loop' is used to tackle this range.

2.If the sum of the digits of the number is equal to 1, it is a happy number.

3. But if sum of the digits of the number is not equal to 1, then two conditions can happen:

a> We can get some number which is already obtained in some previous calculation.This is the terminating condition.

b>We can go on finding the sum of the digits of the number as long as condition 2 or 3<a> is not satisfied.

while(s!=1) takes care of this.

4.Then we summed up the digits of the number and check whether it is already obtained from the string. If not obtained before it is stored in a string where + is used as a delimiter.

## Program

import java.io.*;

public class Happy2

{

public static void main(String args[])

{

try

{

Second sec=new Second();

sec.fun();

}

catch(Exception e)

{

System.out.println(e);

}

}

}

class Second

{

String st,en,ct;

BufferedReader inFromUser,inFromUser1;

int st1,en1,r,s,f,no,i1,flag;

char ch[];

public void fun() throws Exception

{

System.out.println("Enter the Starting range");

inFromUser=new BufferedReader(new InputStreamReader(System.in));

//Take starting number from user

st=inFromUser.readLine();

st1=Integer.parseInt(st); //Convert the string into integer

System.out.println("Enter the Ending range"); //Take ending range from user

inFromUser1=new BufferedReader(new InputStreamReader(System.in));

en=inFromUser1.readLine();

en1=Integer.parseInt(en); //Convert the string into integer

for(int i=st1;i<=en1;i++)

{

flag=0;

s=0;

ct="";

i1=i;

while(s!=1)

//The string terminates if 1 is obtained

{

flag=0;

s=0;

while(i1>0)

//to get the square of every digit of the number

{

r=i1%10;//finding the remainder

f=1;

f=r*r;

s=s+f;

//storing the sum of square of every digit

i1=i1/10;

//finding the quotient of every number

}

i1=s;

ch=ct.toCharArray();//convert the string into array

no=0;

for(int k=0;k<ch.length;k++)

//checking whether the number obtained after summing up every digit of the number is already present

{

if(ch[k]>=48 && ch[k]<=57) //checking whether it is a digit

{

no=no*10+(int)ch[k]-48;//converting the character into digit

}

else

{

if(no==s)//if digit obtained is same as the digit obtained in some previous case

{

flag=1;//then we set a flag value as 1

no=0;

break;

}

no=0;

}

}

if(flag==1)

break;

ct=ct+s+"+";

}

if(flag==0)//if s=1 and if digit obtained is not same as the digit obtained in some previous case

System.out.println(i);

for(int k=0;k<ch.length;k++)

{

ch[k]='\0';//sets the string to null

}

}

}

}

public class Happy2

{

public static void main(String args[])

{

try

{

Second sec=new Second();

sec.fun();

}

catch(Exception e)

{

System.out.println(e);

}

}

}

class Second

{

String st,en,ct;

BufferedReader inFromUser,inFromUser1;

int st1,en1,r,s,f,no,i1,flag;

char ch[];

public void fun() throws Exception

{

System.out.println("Enter the Starting range");

inFromUser=new BufferedReader(new InputStreamReader(System.in));

//Take starting number from user

st=inFromUser.readLine();

st1=Integer.parseInt(st); //Convert the string into integer

System.out.println("Enter the Ending range"); //Take ending range from user

inFromUser1=new BufferedReader(new InputStreamReader(System.in));

en=inFromUser1.readLine();

en1=Integer.parseInt(en); //Convert the string into integer

for(int i=st1;i<=en1;i++)

{

flag=0;

s=0;

ct="";

i1=i;

while(s!=1)

//The string terminates if 1 is obtained

{

flag=0;

s=0;

while(i1>0)

//to get the square of every digit of the number

{

r=i1%10;//finding the remainder

f=1;

f=r*r;

s=s+f;

//storing the sum of square of every digit

i1=i1/10;

//finding the quotient of every number

}

i1=s;

ch=ct.toCharArray();//convert the string into array

no=0;

for(int k=0;k<ch.length;k++)

//checking whether the number obtained after summing up every digit of the number is already present

{

if(ch[k]>=48 && ch[k]<=57) //checking whether it is a digit

{

no=no*10+(int)ch[k]-48;//converting the character into digit

}

else

{

if(no==s)//if digit obtained is same as the digit obtained in some previous case

{

flag=1;//then we set a flag value as 1

no=0;

break;

}

no=0;

}

}

if(flag==1)

break;

ct=ct+s+"+";

}

if(flag==0)//if s=1 and if digit obtained is not same as the digit obtained in some previous case

System.out.println(i);

for(int k=0;k<ch.length;k++)

{

ch[k]='\0';//sets the string to null

}

}

}

}

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