Add SwapAdjacentBits algorithm (#5634)

Author: DarkMatter-999

src/main/java/com/thealgorithms/bitmanipulation/SwapAdjacentBits.java

@@ -0,0 +1,26 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Swap every pair of adjacent bits of a given number.
+ * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ */
+
+public final class SwapAdjacentBits {
+    private SwapAdjacentBits() {
+    }
+
+    public static int swapAdjacentBits(int num) {
+        // mask the even bits (0xAAAAAAAA => 10101010...)
+        int evenBits = num & 0xAAAAAAAA;
+
+        // mask the odd bits (0x55555555 => 01010101...)
+        int oddBits = num & 0x55555555;
+
+        // right shift even bits and left shift odd bits
+        evenBits >>= 1;
+        oddBits <<= 1;
+
+        // combine shifted bits
+        return evenBits | oddBits;
+    }
+}

src/test/java/com/thealgorithms/bitmanipulation/SwapAdjacentBitsTest.java

@@ -0,0 +1,22 @@
+package com.thealgorithms.bitmanipulation;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+class SwapAdjacentBitsTest {
+
+    @ParameterizedTest
+    @CsvSource({
+        "2, 1", // 2 (10 in binary) should become 1 (01 in binary)
+        "43, 23", // 43 should become 23
+        "153, 102", // 153 should become 102
+        "15, 15", // 15 (1111) remains 15 (1111)
+        "0, 0" // 0 (0000) remains 0 (0000)
+    })
+    void
+    testSwapAdjacentBits(int input, int expected) {
+        assertEquals(expected, SwapAdjacentBits.swapAdjacentBits(input));
+    }
+}