#### Kaprekar Numbers

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```package com.thealgorithms.maths;

import java.math.BigInteger;
import java.util.*;

public class KaprekarNumbers {

/* 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
public static ArrayList<Long> kaprekarNumberInRange(long start, long end)
throws Exception {
long n = end - start;
if (n < 0) throw new Exception("Invalid range");
ArrayList<Long> list = new ArrayList<>();

for (long i = start; i <= end; i++) {
}

return list;
}

// Checks whether a given number is Kaprekar Number or not
public static boolean isKaprekarNumber(long num) {
String number = Long.toString(num);
BigInteger originalNumber = new BigInteger(number);
BigInteger numberSquared = originalNumber.multiply(originalNumber);
if (number.length() == numberSquared.toString().length()) {
return number.equals(numberSquared.toString());
} else {
BigInteger leftDigits1 = new BigInteger("0");
BigInteger leftDigits2;
if (numberSquared.toString().contains("0")) {
leftDigits1 =
new BigInteger(
numberSquared
.toString()
.substring(0, numberSquared.toString().indexOf("0"))
);
}
leftDigits2 =
new BigInteger(
numberSquared
.toString()
.substring(
0,
(
numberSquared.toString().length() -
number.length()
)
)
);
BigInteger rightDigits = new BigInteger(
numberSquared
.toString()
.substring(
numberSquared.toString().length() - number.length()
)
);
String x = leftDigits1.add(rightDigits).toString();
String y = leftDigits2.add(rightDigits).toString();
return (number.equals(x)) || (number.equals(y));
}
}
}
```