Problem: Message Route (CSES). There are N computers numbered 1 to N and M bidirectional connections. Find the shortest path from computer 1 to computer N. If a path exists, print its length and the nodes along the path. If no path exists, print IMPOSSIBLE.
This is a textbook BFS problem. Run BFS from node 1. If you reach node N, reconstruct the path using a parent array. If BFS finishes without reaching N, the answer is IMPOSSIBLE. The challenge here is path reconstruction, not finding the distance.