**hard interview questions**node. If you have not read the question, the following will make no sense to you:

`(b & (b-1)) == 0`

Visit the **counting 1 bits** node for a good explanation of why this works.

See all of Power of Two solution, there are 2 more in this node.

This is the solution to problem 9 on the **hard interview questions** node. If you have not read the question, the following will make no sense to you:

`(b & (b-1)) == 0`

Visit the **counting 1 bits** node for a good explanation of why this works.