Pathfinder

A cs1lib app that draws a Dartmouth campus map and, when the user picks two locations, highlights the shortest walk between them. load_graph reads dartmouth_graph.txt in two passes — first building a Vertex for each name; neighbors; x,y line, then wiring up every adjacency list — into a name-to-Vertex dictionary. Each Vertex carries its pixel position, its neighbors, and a backpointer; mouse_press sets the start node and mouse_move tracks the goal under the cursor.

The map is a graph, so breadth-first search finds the fewest-edge route. bfs walks a deque frontier out from the start in rings of increasing distance, stamping a backpointer on each newly reached vertex; the first time it pops the goal, that path is minimal in edges. Following backpointers from the goal back to the start recovers path_used, and draw_connections paints those edges red (with the live frontier in yellow) over the map.