parity done

Author: Ram swaroop

src/me/ramswaroop/bits/Parity.java

@@ -0,0 +1,70 @@
+package me.ramswaroop.bits;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 6/3/15
+ * @time: 3:50 PM
+ */
+
+/**
+ * PARITY: Parity of a number refers to whether it
+ * contains an odd or even number of 1-bits. The number
+ * has “odd parity”, if it contains odd number of 1-bits
+ * and is “even parity” if it contains even number of 1-bits.
+ */
+public class Parity {
+
+    /**
+     * Uses BRIAN KERNIGAN'S bit counting. The time complexity is
+     * proportional to the number of bits set.
+     * {@see http://stackoverflow.com/questions/12380478/bits-counting-algorithm-brian-kernighan-in-an-integer-time-complexity}
+     *
+     * @param n
+     * @return
+     */
+    public static boolean isEvenParity(long n) {
+        boolean parity = true;
+
+        while (n > 0) {
+            parity = !parity;
+            n = n & (n - 1);
+        }
+        return parity;
+    }
+
+
+    /**
+     * Old school method
+     *
+     * @param n
+     * @return true if {@param n} has even number of 1-bits
+     */
+    public static boolean isEvenParityByCountingSetBits(long n) {
+        int setBitsCount = 0;
+
+        while (n > 0) {
+            if ((n & 1) == 1) setBitsCount++;
+            n >>= 1;
+        }
+
+        return setBitsCount % 2 == 0;
+    }
+
+    public static void main(String a[]) {
+        System.out.println(isEvenParity(0));
+        System.out.println(isEvenParity(1));
+        System.out.println(isEvenParity(5));
+        System.out.println(isEvenParity(6));
+        System.out.println(isEvenParity(7));
+        System.out.println(isEvenParity(12));
+        System.out.println("==========================");
+        System.out.println(isEvenParityByCountingSetBits(0));
+        System.out.println(isEvenParityByCountingSetBits(1));
+        System.out.println(isEvenParityByCountingSetBits(5));
+        System.out.println(isEvenParityByCountingSetBits(6));
+        System.out.println(isEvenParityByCountingSetBits(7));
+        System.out.println(isEvenParityByCountingSetBits(12));
+    }
+}