He needed a help from a friend to get this right. I'd argue that at the time of the interview he wasn't ready. I'd also argue that the basic linear solution for

He needed a help from a friend to get this right. I'd argue that at the time of the interview he wasn't ready. I'd also argue that the basic linear solution for this problem is straightforward, doesn't require any clever tricks, and a qualified candidate would have no problem solving it.