Pugh: skip lists as a probabilistic alternative to balanced trees

What changed

Introduced randomized multilevel skip lists with expected logarithmic operations.

Scientific scope

The record is Pugh’s sole-author 1990 Communications of the ACM paper. Its guarantees are probabilistic rather than worst-case balanced-tree guarantees, and later concurrent, deterministic and distributed variants remain separate.

Evidence

The linked sources identify this contribution and its scope. WRS has not independently reconstructed the scientific claims. The record is Pugh’s sole-author 1990 Communications of the ACM paper. Its guarantees are probabilistic rather than worst-case balanced-tree guarantees, and later concurrent, deterministic and distributed variants remain separate.

Contributors

• William Pugh · SCIENCE: Named source author of the scoped work; individual effort shares are not measured.

• ACM DOI for skip lists
• Full copy of Pugh skip-list paper

Provisional WRS assessment, edition 2026-10-16.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.

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