Kaprekar.java

import java.io.*;
class Kaprekar
{
   public static void main(String args[]) throws IOException
   {
     BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
     System.out.print("Enter a Number : ");
     int n = Integer.parseInt(br.readLine()); //Inputting the number
 
     int sq = n*n; //finding the square of the number  
     String s = Integer.toString(sq); //converting the square into a String
 
     if(sq<=9)
        s = "0"+s; //Adding a zero in the beginning if the square is of single digit
 
     int l = s.length(); //finding the length (i.e. no. of digits in the square).
     int mid = l/2; //finding the middle point
 
     String left=s.substring(0,mid); //extracting the left digits from the square
     String right=s.substring(mid); //extracting the right digits from the square
 
     int x = Integer.parseInt(left); //converting the left String into Integer
     int y = Integer.parseInt(right); //converting the right String into Integer
 
     //if sum of left and right numbers is equal to the original number then it is a Kaprekar number
     if(x+y == n) 
        System.out.println(n+" is a Kaprekar Number");
     else
        System.out.println(n+" is Not a Kaprekar Number");
   }
}