Graphs medium time O(V + E) space O(V)
Breadth-First Search
BFS visits everything one step away, then everything two steps away, and so on. A queue holds the frontier, and marking nodes seen the moment they are enqueued stops the same node being queued twice. On an unweighted graph this finds shortest paths.
BFS from A: the queue starts holding just the source.
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A fixed scene — scrub through it, or open the code.
Practice
Machine twin: /dsa-viz-v2/graph-bfs.json — the full deterministic run as structured data.