Unusual Speed Difference between Python and C++

Question

I recently wrote a short algorithm to calculate happy numbers in python. The program allows you to pick an upper bound and it will determine all the happy numbers below it.

Answer 1

Why is everyone using a vector in the c++ version? Lookup time is O(N).

Even though it's not as efficient as the python set, use std::set. Lookup time is O(log(N)).