CTCI 5.07: PairwiseSwap.groovy

src/main/groovy/Ch05_BitManipulation/_05_07_PairwiseSwap.groovy

@@ -0,0 +1,10 @@
+package Ch05_BitManipulation
+
+/** Determine the number of different bits in two numbers */
+class _05_07_PairwiseSwap {
+    /** Complexity: O(1) */
+    private static ODD_MASK = 0b01010101_01010101_01010101_01010101
+    static swapOddEvenBits(int num) {
+        ((num >> 1) & ODD_MASK) | ((num & ODD_MASK) << 1)
+    }
+}

src/test/groovy/Ch05_BitManipulation/_05_07_PairwiseSwapTest.groovy

@@ -0,0 +1,33 @@
+package Ch05_BitManipulation
+
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static Ch05_BitManipulation._05_07_PairwiseSwap.swapOddEvenBits
+
+@Unroll class _05_07_PairwiseSwapTest extends Specification {
+    /*@formatter:off*/
+    def 'swap #source == #target?'() {
+        expect: swapOddEvenBits(source) == target 
+        where:  source || target  
+                0b0000 || 0b0000  
+                0b0001 || 0b0010  
+                0b0010 || 0b0001  
+                0b0011 || 0b0011  
+                0b0100 || 0b1000  
+                0b0101 || 0b1010  
+                0b0110 || 0b1001  
+                0b0111 || 0b1011  
+                0b1000 || 0b0100  
+                0b1001 || 0b0110  
+                0b1010 || 0b0101  
+                0b1011 || 0b0111  
+                0b1100 || 0b1100  
+                0b1101 || 0b1110  
+                0b1110 || 0b1101  
+                0b1111 || 0b1111  
+
+                0b1001010101001010 || 0b0110101010000101
+    }
+    /*@formatter:on*/
+}