the solution of problem "Power of Four"

README.md

@@ -12,7 +12,8 @@ LeetCode
 |349|[Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/) | [C++](./algorithms/cpp/intersectionOfTwoArrays/intersectionOfTwoArrays.cpp)|Easy|
 |347|[Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | [C++](./algorithms/cpp/topKFrequentElements/topKFrequentElements.cpp)|Medium|
 |345|[Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/) | [C++](./algorithms/cpp/reverseVowelsOfAString/reverseVowelsOfAString.cpp)|Easy|
-|345|[Reverse String](https://leetcode.com/problems/reverse-string/) | [C++](./algorithms/cpp/reverseString/ReverseString.cpp)|Easy|
+|344|[Reverse String](https://leetcode.com/problems/reverse-string/) | [C++](./algorithms/cpp/reverseString/ReverseString.cpp)|Easy|
+|342|[Power of Four](https://leetcode.com/problems/power-of-four/) | [C++](./algorithms/cpp/powerOfFour/PowerOfFour.cpp)|Easy|
 |337|[House Robber III](https://leetcode.com/problems/house-robber-iii/) | [C++](./algorithms/cpp/houseRobber/houseRobberIII.cpp)|Medium|
 |334|[Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/) | [C++](./algorithms/cpp/increasingTripletSubsequence/increasingTripletSubsequence.cpp)|Medium|
 |330|[Patching Array](https://leetcode.com/problems/patching-array/) | [C++](./algorithms/cpp/patchingArray/PatchingArray.cpp)|Medium|

algorithms/cpp/powerOfFour/PowerOfFour.cpp

@@ -0,0 +1,37 @@
+// Source : https://leetcode.com/problems/power-of-four/
+// Author : Hao Chen
+// Date   : 2016-05-29
+
+/*************************************************************************************** 
+ *
+ * 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?
+ * 
+ * Credits:Special thanks to @yukuairoy  for adding this problem and creating all test 
+ * cases.
+ ***************************************************************************************/
+
+
+class Solution {
+public:
+    bool isPowerOfFour(int num) {
+        static int mask = 0b01010101010101010101010101010101;
+        
+        //edge case
+        if (num<=0) return false;
+        
+        // there are multiple bits are 1
+        if ((num & num-1) != 0) return false;
+        
+        // check which one bit is zero, if the place is 1 or 3 or 5 or 7 or 9...,
+        // then it is the power of 4
+        if ((num & mask) != 0) return true;
+        return false;
+    }
+};