KaprekarNumbers.java

packagecom.thealgorithms.maths;

importjava.math.BigInteger;
importjava.util.ArrayList;
importjava.util.List;

publicfinalclassKaprekarNumbers {
privateKaprekarNumbers() {
 }

/* This program demonstrates if a given number is Kaprekar Number or not.
 Kaprekar Number: A Kaprekar number is an n-digit number which its square can be split into
 two parts where the right part has n digits and sum of these parts is equal to the original
 number. */

// Provides a list of kaprekarNumber in a range
publicstaticList<Long> kaprekarNumberInRange(longstart, longend) throwsException {
longn = end - start;
if (n < 0) {
thrownewException("Invalid range");
 }
ArrayList<Long> list = newArrayList<>();

for (longi = start; i <= end; i++) {
if (isKaprekarNumber(i)) {
list.add(i);
 }
 }

returnlist;
 }

// Checks whether a given number is Kaprekar Number or not
publicstaticbooleanisKaprekarNumber(longnum) {
Stringnumber = Long.toString(num);
BigIntegeroriginalNumber = BigInteger.valueOf(num);
BigIntegernumberSquared = originalNumber.multiply(originalNumber);
if (number.length() == numberSquared.toString().length()) {
returnnumber.equals(numberSquared.toString());
 } else {
BigIntegerleftDigits1 = BigInteger.ZERO;
BigIntegerleftDigits2;
if (numberSquared.toString().contains("0")) {
leftDigits1 = newBigInteger(numberSquared.toString().substring(0, numberSquared.toString().indexOf("0")));
 }
leftDigits2 = newBigInteger(numberSquared.toString().substring(0, (numberSquared.toString().length() - number.length())));
BigIntegerrightDigits = newBigInteger(numberSquared.toString().substring(numberSquared.toString().length() - number.length()));
Stringx = leftDigits1.add(rightDigits).toString();
Stringy = leftDigits2.add(rightDigits).toString();
return (number.equals(x)) || (number.equals(y));
 }
 }
}