From 98656cb0cdacd175559272bcbb8bc3b86ddac52a Mon Sep 17 00:00:00 2001
From: s-devran <78323181+s-devran@users.noreply.github.com>
Date: Wed, 15 Dec 2021 17:55:04 +0300
Subject: [PATCH] Add Kaprekar Numbers (#2881)

---
 .../thealgorithms/maths/KaprekarNumbers.java  | 27 +++++++++
 .../maths/KaprekarNumbersTest.java            | 58 +++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/maths/KaprekarNumbers.java
 create mode 100644 src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java

diff --git a/src/main/java/com/thealgorithms/maths/KaprekarNumbers.java b/src/main/java/com/thealgorithms/maths/KaprekarNumbers.java
new file mode 100644
index 000000000..c922ab25d
--- /dev/null
+++ b/src/main/java/com/thealgorithms/maths/KaprekarNumbers.java
@@ -0,0 +1,27 @@
+package com.thealgorithms.maths;
+
+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. */
+
+	// Checks whether a given number is Kaprekar Number or not
+
+	public static boolean isKaprekarNumber(long number) {			
+		long numberSquared = number * number;
+		if(Long.toString(number).length() == Long.toString(numberSquared).length()){
+			return (number == numberSquared);
+		}
+		else{
+			long leftDigits1 = 0, leftDigits2 = 0;
+			if(Long.toString(numberSquared).contains("0")){
+				leftDigits1 = Long.parseLong(Long.toString(numberSquared).substring(0, Long.toString(numberSquared).indexOf("0")));
+			}
+			leftDigits2 = Long.parseLong(Long.toString(numberSquared).substring(0, (Long.toString(numberSquared).length() - Long.toString(number).length())));
+			long rightDigits = Long.parseLong(Long.toString(numberSquared).substring(Long.toString(numberSquared).length() - Long.toString(number).length()));
+			return (number == (leftDigits1 + rightDigits)) || (number == (leftDigits2 + rightDigits));
+		}		
+	}
+
+}
diff --git a/src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java b/src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java
new file mode 100644
index 000000000..04f8cc09b
--- /dev/null
+++ b/src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java
@@ -0,0 +1,58 @@
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class KaprekarNumbersTest {
+
+	@Test
+	void testFor1() 
+	{
+		assertTrue(KaprekarNumbers.isKaprekarNumber(1));
+	}
+
+	@Test
+	void testFor45() 
+	{
+		assertTrue(KaprekarNumbers.isKaprekarNumber(45));
+	}
+
+	@Test
+	void testFor297() 
+	{
+		assertTrue(KaprekarNumbers.isKaprekarNumber(297));
+	}
+
+	@Test
+	void testFor2223() 
+	{
+		assertTrue(KaprekarNumbers.isKaprekarNumber(2223));
+	}
+
+	@Test
+	void testFor857143() 
+	{
+		assertTrue(KaprekarNumbers.isKaprekarNumber(857143));
+	}
+
+
+	@Test
+	void testFor3() 
+	{
+		assertFalse(KaprekarNumbers.isKaprekarNumber(3));
+	}
+
+	@Test
+	void testFor26() 
+	{
+		assertFalse(KaprekarNumbers.isKaprekarNumber(26));
+	}
+
+	@Test
+	void testFor98() 
+	{
+		assertFalse(KaprekarNumbers.isKaprekarNumber(98));
+	}
+
+}
\ No newline at end of file