Needs random tests.

main.cpp:25:1: error: no template named 'vector'; did you mean 'std::vector'?
vector<int> allNums;

Duplicate of at least https://www.codewars.com/kata/5eb9cf981e46ba0029087c38 and probably another approved kata.

Including a non-standard header in the initial solutions probably isn't the best idea...

main.cpp:19:1: error: no template named 'vector'; did you mean 'std::vector'?
vector<int> allNums;