I have a program which is supposed to find the shortest path between airports and users' flight data to find the shortest path between airports; that is, the airports are the nodes and the flights are the edges.

I've not started to implement the algorithm as yet but I am working on the implementation of the airports and the flights.

Unfortunately, my program crashes when I am testing. I've put in debug statements in the code to find out where and why it's crashing but, unfortunately, I'm having a hard time.

I am going to attach the files if anyone could please tell me where I've gone wrong that would be greatly appreciated. Thanks.