is power of four

Author: jackzhenguo

BinaryManipulation/PowOfFourSln.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BinarySearch.Lib
+{
+// Given an integer (signed 32 bits), write a function to check whether it is a power of 4.
+
+// Example:
+// Given num = 16, return true. Given num = 5, return false.
+
+// Follow up: Could you solve it without loops/recursion?
+public class Solution 
+{
+    public bool IsPowerOfFour(int num) 
+	{
+        //4d: 0010Binary 3d: 1100  0010 & 1100 = 0
+        //16d:00001      15d: 11110 00001 & 11110 = 0
+        return (num&(num-1)) == 0 && (num & 0x55555555) != 0;
+        //0x55555555 is to remove those power of 2 but not power of 4
+        //so that the value 1 always appears at the odd index 
+    }
+}
+}