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// 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;

}

};