Description
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?
Solution
在判断2^x的基础上再使用一个mask就好啦。
Bit operation, time O(1), space O(1)
class Solution {
public boolean isPowerOfFour(int num) {
return num > 0 && (num & (num - 1)) == 0
&& (num & 0x55555555) == num;
}
}
