Editorial

Solution walkthrough

Review the explanation, then compare the reference implementation.

Video explanation

Solution

Intuition

A positive power of two has exactly one set bit. Subtracting one clears its lowest set bit and turns all lower zero bits into ones. Consequently, n & (n - 1) removes the lowest set bit from any positive integer and becomes zero exactly when no other set bit exists.

Approach

Reject zero and negative values; neither can be a power of two under this definition.
Compute the bitwise AND of n and n - 1.
Return whether that value is zero. The positivity check is essential because zero also satisfies the bitwise equality. The value one is accepted, representing 2^0.

class Solution:
    def isPowerOfTwo(self, n: int) -> bool:
        if n <= 0:
            return False
        return not (n & n - 1)

Complexity analysis

The single bit test uses O(1) time and O(1) auxiliary space.