Match the traversal to what you actually want to learn. Both visit every reachable vertex in O(V + E) time, so the choice is about order and memory, not raw speed. BFS explores by distance; DFS explores by depth.
Reach for BFS when nearness matters. It finds the fewest-edge path, works well for "closest match" and level-by-level problems, and suits shallow, wide searches. Reach for DFS when structure matters. It fits cycle detection, connected components, and topological sort, where you want to fully explore each branch.
Memory is the other tiebreaker.
- BFS holds a whole frontier, which can be huge on wide graphs
- DFS holds only the current path, but recursion can overflow on very deep graphs
So a rough rule: if you care about shortest hops or the answer is likely nearby, use BFS. If you care about the graph's overall shape, use DFS.
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