added program for evil number

Author: TaranjeetSinghKalsi

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

@@ -0,0 +1,39 @@
+package com.thealgorithms.maths;
+
+/**
+ * In number theory, an evil number is a non-negative integer that has an even number of 1s in its binary expansion.
+ * Non-negative integers that are not evil are called odious numbers.
+ *
+ * Evil Number Wiki: https://en.wikipedia.org/wiki/Evil_number
+ * Odious Number Wiki: https://en.wikipedia.org/wiki/Odious_number
+ */
+public final class EvilNumber {
+
+    private EvilNumber() {
+    }
+
+    // Function to count number of one bits in a number using bitwise operators
+    private static int countOneBits(int number) {
+        int oneBitCounter = 0;
+        while (number > 0) {
+            oneBitCounter += number & 1; // increment count if last bit is 1
+            number >>= 1; // right shift to next bit
+        }
+        return oneBitCounter;
+    }
+
+    /**
+     * Check either {@code number} is an Evil number or Odious number
+     *
+     * @param number the number
+     * @return {@code true} if {@code number} is an Evil number, otherwise false (in case of of Odious number)
+     */
+    public static boolean isEvilNumber(int number) {
+        if (number < 0) {
+            throw new IllegalArgumentException("Negative numbers are not allowed.");
+        }
+
+        int noOfOneBits = countOneBits(number);
+        return noOfOneBits % 2 == 0;
+    }
+}

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

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+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+class EvilNumberTest {
+    @ParameterizedTest
+    @CsvSource({"0", "3", "10", "129", "222", "500", "777", "1198"})
+    void evilNumbersTest(int n) {
+        assertTrue(EvilNumber.isEvilNumber(n));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"1", "7", "100", "333", "555", "1199"})
+    void odiousNumbersTest(int n) {
+        assertFalse(EvilNumber.isEvilNumber(n));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"-1"})
+    void throwsNegativeNumbersNotAllowed(int n) {
+        assertThrows(IllegalArgumentException.class, () -> EvilNumber.isEvilNumber(n));
+    }
+}