342. Power of Four

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example 1:

Input: 16

Output: true

Example 2:

Input: 5

Output: false

Follow up: Could you solve it without loops/recursion?

 

思路参考这里

4的幂一定是2的幂，并且二进制中1一定在奇数位

class Solution { public: bool isPowerOfFour(int num) { return num>0&&(num&(num-1))==0&&(num&0x55555555); } };