342. Power of Four【easy】【python】

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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题目要求判断是不是4的幂。可以利用判断是否是2的幂的方法。

如果一个整数num是2的幂，则num&(num-1）==0,2的幂自然是4的幂，只需要再添加一个条件，即：二进制的num中0的个数是偶数个即可。

代码：

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