Power of Two - Implementation

Here's the complete solution:

function isPowerOfTwo(n)
    if n ≤ 0 then
        return false
    return (n & (n - 1)) = 0

First, handle the edge case: non-positive numbers cannot be powers of 2. Then check if $n \& (n-1) = 0$. This works because powers of 2 have exactly one bit set. Time: $O(1)$. Space: $O(1)$.