Checkpoint — Restate, Then Sweep

Checkpoint — Restate, Then Sweep. "Remove the fewest intervals" is the reframed objective: equivalently, keep the maximum number of non-overlapping intervals — the classic exchange-argument structure (sort by right endpoint; keeping the earliest-ending survivor never hurts). The W is the plausible sort-by-left greedy: it keeps a long early interval that shadows several short later ones. On the mixed test the two diverge — construction, not luck.