Leetcdoe-342. Power of 4

An operation

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Topic details

Given an integer , Write a function to determine if it is 4 Power square . If it is , return true ; otherwise , return false .
Integers n yes 4 To the power of ： There are integers x bring n == 4^x

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Example 1：

 Input ：n = 16
 Output ：true

Example 2:

 Input ：n = 5
 Output ：false

Example 3:

 Input ：n = 1
 Output ：true

Ideas :
When a number n yes 2 Integer power of : Then its binary must be 0...010...0 Form like this ( Only one is 1)
n-1 The binary of is 0...001...1 You can get : n & (n-1) == 0 ==> This number is 2 Integer power of
So if n It's also 4 The integer power of ? So the binary 1 The position of must be odd ( And only this one ), for example 0...01
0...1000...10000 Title n The range is -2^31 <= n <= 2^31 - 1 Binary 32 position
So we can use 10101...101(32 The odd digits are all 1 Even digits are all 0) Give Way n Do and calculate with it
If the result is not 0 explain n There is one odd digit in the binary of 1, namely n yes 4 Integer power of

My code ：

class Solution 
{
    
public:
    bool isPowerOfFour(int n) 
    {
    
        // n by 2 Integer power of  10101...101 The hexadecimal representation of 
        return n > 0 && !(n & (n - 1)) && (n & 0x55555555); 
    }
};

Common skills of bit operation