Distribute a 10GB file from one bandwidth-constrained source to thousands of interconnected hosts, minimizing time to completion.

The core insight the question screens for is that naive fan-out (every host pulls from the source) makes completion time scale linearly with N because the source's uplink is the bottleneck, while a peer swarm makes it scale roughly logarithmically because capacity grows with the swarm. Strong candidates chunk the file, let peers exchange pieces, and pick a piece-selection strategy (rarest-first) so the source's bits propagate and no piece becomes a single point of failure. The reserve probes are usually verification (per-chunk hashes from a signed manifest, not one hash at the end) and topology (rack/zone locality to avoid hammering cross-datacenter links). Watch for candidates who reinvent BitTorrent badly: no piece selection, so everyone grabs piece 0 and the tail drags; or trusting peer data without per-chunk verification.