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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題目要求判斷是不是4的冪?？梢岳门袛嗍欠袷?的冪的方法。

如果一個整數num是2的冪，則num&(num-1）==0,2的冪自然是4的冪，只需要再添加一個條件，即：二進制的num中0的個數是偶數個即可。

代碼：

return num&(num-1)==0 and len(str(bin(num)[3:]))%2==0