Question

write a program in Java to input a number and check whether it is a kaprekar number or not ​

Answer 1

A positive whole number ‘n’ that has ‘d’ number of digits is squared and split into two pieces, a right-hand piece that has ‘d’ digits and a left-hand piece that has remaining ‘d’ or ‘d-1’ digits.

If the sum of the two pieces is equal to the number, then ‘n’ is a Kaprekar number. The first few Kaprekar numbers are: 9, 45, 297 ……..

Example 1:

92 = 81, right-hand piece of 81 = 1 and left hand piece of 81 = 8

Sum = 1 + 8 = 9, i.e. equal to the number. Hence, 9 is a Kaprekar number.

Example 2:

452 = 2025, right-hand piece of 2025 = 25 and left hand piece of 2025 = 20

Sum = 25 + 20 = 45, i.e. equal to the number. Hence, 45 is a Kaprekar number.

Example 3:

2972 = 88209, right-hand piece of 88209 = 209 and left hand piece of 88209 = 88

Sum = 209 + 88 = 297, i.e. equal to the number. Hence, 297 is a Kaprekar number.

Program :-

import java.util.*;

class Kaprekar

{

public static void main(String args[]) throws IOException

{

Scanner sc = new Scanner(System.in);

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

int n = sc.nextInt(); //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");

}

}