Power of Four - LeetCode

题意

Given an integer n, return *true if it is a power of four. Otherwise, return false*.

An integer n is a power of four, if there exists an integer x such that n == 4x.

Example 1:

Input: n = 16
Output: true

Example 2:

Input: n = 5
Output: false

Example 3:

Input: n = 1
Output: true

Constraints:

• 231 <= n <= 231 - 1

Follow up:

Could you solve it without loops/recursion?

思路

1. 常规
2. 位运算：二进制表示应该是 1 00 00 00的形式，也就是它只有一个1，而且1的位置有要求，只能在01010101的上面，也就是0x55。

题解

class Solution:
    def isPowerOfFour(self, n: int) -> bool:
        return n > 0 and (n & (n - 1)) == 0 and (n & 0x55555555) != 0