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.

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class Solution {
public:
	bool isPowerOfFour(int num) {
		if(num < 1) return false;

		if(num == 1 || num == 4) return true;
		if(num%4 > 0 && num%4 < 4) return false;

		return isPowerOfFour(num/4);
	}
}