342. Power of Four

题目：

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?

答案：

判断一个数是否是4的幂，不能使用循环和递归：

前面我们已经做过一个数是否为2的幂这道题，4的幂跟2的幂一样，都是最高位为1，其他位为0。

不同的是4的幂中的1在偶数位上，所以我们可以用0xaaaaaaaa与之按位与。

1 class Solution {
2 public:
3     bool isPowerOfFour(int num) {
4         return num>0&&(!(num&(num-1)))&&(!(num&(0xaaaaaaaa)));
5     }
6 };

时间： 2024-08-02 20:58:06

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