JS how to determine whether a number is 2 n power

Yesterday to interview, the interviewer asked an interview question, said how to determine whether a number is 2 of the n power, I did not know that 2 of the power of the n is what (embarrassing big?? ), it's okay to explain it to me. Finally go home on the internet to look up data, collated a method.

Method One

How to determine whether a number is a 2 of the N power, the simple method of judging is this number num directly except 2, if the remainder is 0, then NUM/2 2, and then determine whether the remainder is 0, is the words continue to press the previous step, until the last for the num=1.

For example: 2 2%2=0 (2/2) =1 is

4 4%2=0 (4/2)%2=0 (4/2/2) =1 Yes

6 6%2=0 (6/2)%2=1 not

7 7%2=1 not

24 24%2=0 (24/2)%2=0 (24/2/2)%2=0 (24/2/2/2)%2=1 not

Code implementation:

functionCheck (num) {if(num! = 1){         while(num! = 1){            if(num%2 = = 0) {num= NUM/2; }Else{                return false; }        }        return true; }Else{        return true; }}

The results are as follows:

Method Two

The binary method can be used to determine whether a number num is 2 n power, the law is known, as long as the power of 2, it is bound to be the highest bit 1, the remaining 0, when num-1, the highest bit is 0, the remaining 1.

Bitwise AND Operation: 1&1=1 0&1=0 0&0=0 1&0=0

2---> 3---> 11

4---> 6---> 110

8---> 7---> 111

Example: Binary 1000 8-1 of binary 0111 bitwise AND Operation 1000&0111 8--and 0000 so 8 is the n power of 2.

Binary 1001 of 9 binary 1000 Bitwise AND operation 1001&1000---> 1000 so 9 is not a power of 2.

Binary 11000 of 24 binary 10111 bitwise AND operation 11000&10111---> 10000 so 24 is not a power of 2.

You can write the binary of Num by num.tostring (2).

Code implementation:

function Check (num) {    return (num > 0) && ((Num & (num-1)) = = 0);}

The results are as follows:

The other 1 is also 2 of the 0 power.

There are other conditions not written, this method is to determine whether a number is 2 n power, and did not write this number is not an integer, you can add the condition to judge.

JS how to determine whether a number is 2 n power