Leetcode 342. Power of Four

Given an Integer (signed), write a function to check whether it is a power of 4.

Example: Given num = +, return true. Given num = 5, return false.

followup: Could solve it without loops/recursion?

Main topic:

Given an integer (32-bit signed), the Write function determines whether it is a power of 4.

Test with For example a topic description.

think further: can you solve the problem without looping/recursion?

Problem Solving Ideas:

If an integer is a power of 4, then the second binary form (only one 1, 0 on odd digits) has the following characteristics:

1. The highest bit is 1 and the remaining bits are 0

2.0 is an even number

Condition 1 can be judged with num & (num-1) = = 0

Condition 2 can be judged with num & 0x55555555 > 0, (0x55555555) <==> 1010101010101010101010101010101, if the obtained number is itself, You can be sure that it is 4 of the number of times:

1 classSolution {2  Public:3     BOOLIspoweroffour (intnum) {4         if(num<=0)return false;5         Else return((num& (num-1))==0) && (num&0x55555555)==num);6     }7};

Using the Loop method:

1 classSolution {2  Public:3     BOOLIspoweroffour (intnum) {
if (num < 0) return false;4         intNumofone =0;5          while(num > 0) {6             if(Num &1)7numofone++;8             if(Num >>1) &1)9                 return false;TenNum >>=2; One         } A         if(Numofone = =1) -             return true; -         Else the             return false; -     } -};

Leetcode 342. Power of Four