Count Same-Bit Numbers

OA combinatorics problem: for `n`, count integers up to the next all-ones bitmask that have the same number of set bits as `n`, excluding `n` itself. Requirements For any positive integer n, define f(n) as the smallest integer greater than or equal to n in which all bits are set to 1. Given a positive integer n, count integers other than n that are <= f(n) and have the same number of set bits as n. Meet the stated complexity requirement. Bitwise reasoning plus combinatorics passed the reported OA. Notes Convert f(n) into the all-ones mask at n's bit length. The count is a combinations problem over bit positions, then subtract the original n.