How to check if a number is power of 2 ?

Solution #1. Divide num by 2 recursively
Time complexity : O(log2n)


Solution #2. Using Bitwise & operator with num and num-1
boolean isPowerOf2 = (num & (num-1))==0;

Time complexity : O(1)

Example : 
num = 8
n    = 8 = 1000
n-1 = 7 = 0111
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               0000 => Power of 2, Yes.