Check connectivity between two subway stations
Quick Overview
This problem evaluates graph connectivity and traversal concepts—specifically reasoning about adjacency representations, path existence, cycles, disconnected components, and missing-node edge cases—within the Coding & Algorithms domain at an implementation-level (medium) abstraction.
You are given a description of subway stations A, B, C, D, E, ... as a graph. For each station, you are told which other stations it directly connects to (e.g., an adjacency list/map).
Write a function that, given two station names start and end, returns whether it is possible to travel from start to end by following one or more connections (i.e., whether a path exists).
Assume station names are strings. If a station is not present in the map, treat it as having no outgoing connections.
Additionally, write a few test cases for your function (including cases with cycles, disconnected components, start==end, and missing stations).