Aristocrat interview questions

1st round was written of mcq on C++. After that there was f2f interview. The 2 interviewers were young and did not introduced themselves. Questions were asked related to private virtual function, dynamic cast etc. In between they asked how to group together odd/even integers in an array/vector in O(n) time. I was able to answer 80% of the questions but was still not able to qualify for next round. Might be they were looking for a perfect candidate.