Backtracking and Graphs

Learn — backtracking is choose, recurse, un-choose, and duplicates are handled at the choice. For graphs: BFS for shortest unweighted, DFS for reachability, topological sort for ordering, Dijkstra once edges carry weights.

Do — problems 59–76.

Check — you know why a single visited set wrongly reports a cycle on a diamond dependency; you can say why BFS by hop count is wrong the moment weights differ; you can state why a recursive flood fill on a 300x300 grid blows the stack and what you do instead.

Ship — repo.

The graph problems repeat a small number of shapes. If you find yourself learning each one separately, stop and name the shape instead — that is the whole transfer.