1. Initial technical phone screen with hiring manager, which concluded with a basic offline coding test in the language of choice that takes a few hours to complete.

2. The next step is a non-trivial coding exercise to do at home that can take roughly 5-10 hours.

3. In-person interview with several members of the team.

4. Decision on whether to extend an offer.

Problem:

A traveler flies to many cities (airports) in an unbroken chain of flights with no loops, meaning she never revisits an airport.

For every flight, she has a boarding pass with only a "From" (City) and "To" (City) printed on it, but no date or time.

At the end of her journey, she hands you all her boarding passes, but they are shuffled, so you don’t know the starting or the ending city.

Can you:

Write logic or pseudocode to print her whole journey in sequence. It should print, for example: (Starting) City1 -> City2 -> ... -> (Ending) CityX.

State the time complexity of your solution.

You are given a Set of BoardingPass objects as input.

There could be as many as hundreds of thousands of unique cities/airports.

Memory is no concern (i.e., you have infinite memory!). Optimize for execution time (time complexity).