Module 63 Extra
Graphs
Graphs, for anything made of connections. Adjacency lists built from a list of edges, breadth-first search for the fewest steps on a grid, depth-first search with a stack of your own for flood fill and groups, topological sort for an order to build things in, Dijkstra's algorithm with heapq for weighted routes, and union-find for groups that merge, with big tests where the right algorithm is the fast way.