leetcode brushing notes 342 power of 4

Topic description:

Given an integer (32-bit signed integer type), write a function to check if it is a power of 4.

Example:
When num = 16, return true. When num = 5, return false.

Question Advanced: Can you solve this problem without using loops/recursion?

 

Topic Analysis:

The same idea as the 231 question, or solve this problem through bit operation

First judge the case where the input is 0 and negative

Then analyze the characteristics of powers of 4 0, 4, 16

Convert to binary 0,0100,00010000

The difference from finding the power of 2 is that 2,8 are missing here.

Convert to binary ,0010,00001000

0	0	0	0	0	1	0	0
0	0	0	0	1	0	0	0

  4

  8

 

We try to filter out 2,8 using bit operations

 

Answer code:

C++ version:

class Solution {
public:
    bool isPowerOfFour(int n) {
        if (n<=0) return false;
        return  ((n&(n-1))==0 && ((n&0x55555555)));
    }
};

Code

Python version:

class Solution:
    def isPowerOfFour(self, num):
        """
        :type num: int
        :rtype: bool
        """
        if num<=0:
            return False
        return  ((num&(num-1))==0 and (bool(num&0x55555555)))
        

Code