CSES 1667 Message Route - Problem Statement

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.