Added function to check happy number with testcases

src/main/java/com/thealgorithms/maths/HappyNumber.java

@@ -1,5 +1,7 @@
 package com.thealgorithms.maths;
 
+import java.util.HashSet;
+
 /**
  * A Happy Number is defined as a number which eventually reaches 1 when replaced
  * by the sum of the squares of each digit.
@@ -54,4 +56,21 @@ private static int sumOfSquares(int num) {
         }
         return sum;
     }
+
+    /**
+     * Checks whether the given number is a Happy Number using HashSet to detect cycles.
+     *
+     * @param n The number to check
+     * @return true if n is a Happy Number, false otherwise
+     */
+    public static boolean isHappyNumber(int num) {
+        HashSet<Integer> seen = new HashSet<>();
+
+        while (num != 1 && !seen.contains(num)) {
+            seen.add(num);
+            num = sumOfSquares(num);
+        }
+
+        return num == 1;
+    }
 }

src/test/java/com/thealgorithms/maths/HappyNumberTest.java

@@ -3,30 +3,22 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class HappyNumberTest {
 
-    @Test
-    void testHappyNumbers() {
-        // Known happy numbers
-        assertTrue(HappyNumber.isHappy(1));
-        assertTrue(HappyNumber.isHappy(7));
-        assertTrue(HappyNumber.isHappy(19));
-        assertTrue(HappyNumber.isHappy(100));
+    @ParameterizedTest
+    @CsvSource({"1", "7", "19", "100", "565", "998", "1000000"})
+    void testHappyNumbers(final int n) {
+        assertTrue(HappyNumber.isHappy(n));
+        assertTrue(HappyNumber.isHappyNumber(n));
     }
 
-    @Test
-    void testUnhappyNumbers() {
-        // Known unhappy numbers
-        assertFalse(HappyNumber.isHappy(2));
-        assertFalse(HappyNumber.isHappy(4));
-        assertFalse(HappyNumber.isHappy(20));
-    }
-
-    @Test
-    void testLargeNumber() {
-        // Just to check behavior with larger input
-        assertTrue(HappyNumber.isHappy(1000000)); // reduces to 1 eventually
+    @ParameterizedTest
+    @CsvSource({"2", "4", "20", "300", "999", "9999"})
+    void testUnhappyNumbers(final int n) {
+        assertFalse(HappyNumber.isHappy(n));
+        assertFalse(HappyNumber.isHappyNumber(n));
     }
 }