amphipod

approach

this one is unfinished. the code sets up a search over burrow states: checks for the final arrangement, BFS distances through the hallway, and per-type move costs (A=1, B=10, C=100, D=1000), but the move generation and the search itself stop partway, and it only reads the test input.

the usual route from here is dijkstra over whole board states, where each move is an amphipod walking into the hallway or into its own room.