Prefix Sums (Scan)

Running totals in parallel — the doubling ladder, exclusive scans, and the offsets every variable-sized output depends on.

6 tasks

1. The Sum So Far
2. Everyone Sums Their Own Prefix
3. The Doubling Ladder
4. Inclusive, Exclusive, and Why It Matters
5. Work-Efficient: Upsweep, Downsweep
6. Payoff: Offsets Place the Data

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