It was the first round of a 1-hour phone interview. Before the interview, I was informed about what I was supposed to do in the first round: C++ related questions and a task. I was also provided with a HackerRank link. The interviewer called me on time, and immediately after introducing himself, he started describing the interview task. The interview was going quite well; the interviewer was responsive and helpful. He clearly answered my questions about the performance requirements of the expected solution and so on. I was a bit nervous and spent a lot of time (my bad) thinking about the solution design. Actually, I did not implement the final solution, but it was clear that the interviewer saw my understanding. At the end of the interview, we had a brief talk about how an optimal solution could be implemented.

Given a set of airports and an adjacency matrix that describes whether a route is possible between each pair of airports, implement an algorithm that returns all possible routes between two selected airports.