Un-set the least significant bit

Author: rampatra

src/main/java/com/ctci/bitmanipulation/Conversion.java

@@ -12,7 +12,7 @@ public class Conversion {
      * Example:
      * Input: 29 (or: 11101), 15 (or: 01111)
      * Output: 2
-     * 
+     *
      * @param a
      * @param b
      * @return the number of bits to flip
@@ -32,9 +32,32 @@ private static int countSetBits(int n) {
         return count;
     }
 
+    /**
+     * In this approach, we first take the xor of both the integers (which sets the bits at positions where the bits
+     * in a and b are different). We then unset the least significant bit in each iteration (c & (c - 1)) and count the
+     * number of iterations to find the bits to flip.
+     *
+     * @param a
+     * @param b
+     * @return the number of bits to flip
+     */
+    private static int getNoOfBitsToFlipToConvertAToBWithoutRightShift(int a, int b) {
+        int count = 0;
+        for (int c = a ^ b; c != 0; c = c & (c - 1)) {
+            count++;
+        }
+        return count;
+    }
+
     public static void main(String[] args) {
         System.out.println(getNoOfBitsToFlipToConvertAToB(5, 7));
         System.out.println(getNoOfBitsToFlipToConvertAToB(5, 5));
         System.out.println(getNoOfBitsToFlipToConvertAToB(29, 15));
+
+        System.out.println("---");
+
+        System.out.println(getNoOfBitsToFlipToConvertAToBWithoutRightShift(5, 7));
+        System.out.println(getNoOfBitsToFlipToConvertAToBWithoutRightShift(5, 5));
+        System.out.println(getNoOfBitsToFlipToConvertAToBWithoutRightShift(29, 15));
     }
 }

src/main/java/com/ctci/bitmanipulation/Debugger.java

@@ -0,0 +1,30 @@
+package com.ctci.bitmanipulation;
+
+/**
+ * @author rampatra
+ * @since 2019-03-17
+ */
+public class Debugger {
+
+    /**
+     * If after un-setting the least significant bit in n, it becomes 0 then it implies that it has only set bit. This
+     * can also imply that n is a power of 2.
+     *
+     * @param n input integer
+     * @return {@code true} if n has only set bit, {@code false} otherwise.
+     */
+    private static boolean hasOneSetBit(int n) {
+        // edge case
+        if (n == 0) {
+            return false;
+        }
+        return (n & (n - 1)) == 0; // (n & (n - 1)) un-sets the least significant bit    
+    }
+
+    public static void main(String[] args) {
+        System.out.println(hasOneSetBit(0));
+        System.out.println(hasOneSetBit(2));
+        System.out.println(hasOneSetBit(16));
+        System.out.println(hasOneSetBit(10));
+    }
+}