Research Interests
I'm working on compact data structures, in particular different variants of perfect hashing. A perfect hash function is a function h: S → [m] which has no collisions on a given input set S. On all other inputs, the function is undefined. So in particular, it might have collisions. Furthermore, I am interested in index data structures in general, as well as accelerating algorithms using GPUs.
| Bild | Title | Short Description | Source Code | Corresponding Paper |
|---|---|---|---|---|
| PaCHash | External perfect hash table for objects of variable size |
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| LeMonHash | Monotone Minimal Perfect Hashing based on Retrieval and the PGM-Index |
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| SicHash | A Perfect Hash Function based on irregular cuckoo hashing |
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| ShockHash | Space-efficient perfect hash function based on finding random pseudoforests |
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| GPURecSplit / SIMDRecSplit | Parallelization of a space-efficient minimal perfect hash function |
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| Consensus-RecSplit | Perfect hashing by Combined Search and Encoding of Successful Seeds |
Publications
Lehmann, H.-P.; Sanders, P.; Walzer, S.; Ziegler, J.
2025. A. Benoit, H. Kaplan, S. Wild & G. Herman (Eds.), 33rd Annual European Symposium on Algorithms (ESA 2025), Warschau, 15th-17th September 2025, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (LZI). doi:10.4230/LIPIcs.ESA.2025.109
Hermann, S.; Kirmayer, S.; Lehmann, H.-P.; Sanders, P.; Walzer, S.
2025. A. Benoit, H. Kaplan, S. Wild & G. Herman (Eds.), 33rd Annual European Symposium on Algorithms (ESA 2025), Warschau, 15th-17th September 2025, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (LZI). doi:10.4230/LIPIcs.ESA.2025.99
Lehmann, H.-P.
2024, November 20. Karlsruher Institut für Technologie (KIT). doi:10.5445/IR/1000176432
Hermann, S.; Lehmann, H.-P.; Pibiri, G. E.; Sanders, P.; Walzer, S.
2024. 32nd Annual European Symposium on Algorithms (ESA 2024). Ed.: T. Chan, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (LZI). doi:10.4230/LIPIcs.ESA.2024.69
Lehmann, H.-P.; Sanders, P.; Walzer, S.
2024. 2024 Proceedings of the Symposium on Algorithm Engineering and Experiments (ALENEX).: Ed.: R. Chowdhury, 195–206, Society for Industrial and Applied Mathematics (SIAM). doi:10.1137/1.9781611977929.15
Ferragina, P.; Lehmann, H.-P.; Sanders, P.; Vinciguerra, G.
2023. 31st Annual European Symposium on Algorithms (ESA 2023), Schloss Dagstuhl - Leibniz-Zentrum für Informatik. Ed.: I. Gørtz, 46:1–46:17, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (LZI). doi:10.4230/LIPIcs.ESA.2023.46
Bez, D.; Kurpicz, F.; Lehmann, H.-P.; Sanders, P.
2023. 31st Annual European Symposium on Algorithms (ESA 2023), Schloss Dagstuhl - Leibniz-Zentrum für Informatik. Ed.: I. Gørtz, 19:1–19:16, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (LZI). doi:10.4230/LIPIcs.ESA.2023.19
Kurpicz, F.; Lehmann, H.-P.; Sanders, P.
2023. 2023 Proceedings of the Symposium on Algorithm Engineering and Experiments (ALENEX), 162–175, Society for Industrial and Applied Mathematics (SIAM). doi:10.1137/1.9781611977561.ch14
Lehmann, H.-P.; Sanders, P.; Walzer, S.
2023. 2023 Proceedings of the Symposium on Algorithm Engineering and Experiments (ALENEX), Florence, I, January 22-23,2023, 176–189, Society for Industrial and Applied Mathematics (SIAM). doi:10.1137/1.9781611977561.ch15
Lehmann, H.-P.
2021. Karlsruher Institut für Technologie (KIT). doi:10.5445/IR/1000133378
| Title | Authors | Source | Date |
|---|---|---|---|
| Modern Minimal Perfect Hashing: A Survey | Hans-Peter Lehmann, Thomas Mueller, Rasmus Pagh, Giulio Ermanno Pibiri, Peter Sanders, Sebastiano Vigna, Stefan Walzer |
Juni 2025 | |
| Engineering Minimal k-Perfect Hash Functions | Stefan Hermann, Sebastian Kirmayer, Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
April 2025 | |
| Combined Search and Encoding for Seeds, with an Application to Minimal Perfect Hashing | Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
February 2025 | |
| Brief Announcement: Parallel Construction of Bumped Ribbon Retrieval | Matthias Becht, Hans-Peter Lehmann, Peter Sanders |
November 2024 | |
| PHOBIC: Perfect Hashing with Optimized Bucket Sizes and Interleaved Coding | Stefan Hermann, Hans-Peter Lehmann, Giulio Ermanno Pibiri, Peter Sanders, Stefan Walzer |
April 2024 | |
| Bipartite ShockHash: Pruning ShockHash Search for Efficient Perfect Hashing | Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
October 2023 | |
| ShockHash: Towards Optimal-Space Minimal Perfect Hashing Beyond Brute-Force | Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
August 2023 | |
| Learned Monotone Minimal Perfect Hashing | Paolo Ferragina, Hans-Peter Lehmann, Peter Sanders, Giorgio Vinciguerra |
April 2023 | |
| High Performance Construction of RecSplit Based Minimal Perfect Hash Functions | Dominik Bez, Florian Kurpicz, Hans-Peter Lehmann, Peter Sanders |
December 2022 | |
| SicHash - Small Irregular Cuckoo Tables for Perfect Hashing | Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
October 2022 | |
| PaCHash: Packed and Compressed Hash Tables | Florian Kurpicz, Hans-Peter Lehmann, Peter Sanders |
May 2022 | |
| Weighted Random Sampling on GPUs | Hans-Peter Lehmann, Lorenz Hübschle-Schneider, and Peter Sanders |
June 2021 |
| Title | Conference | Author(s) |
|---|---|---|
| Fast and Space-Efficient Perfect Hashing | Doctoral Defense |
Hans-Peter Lehmann |
| ShockHash: Towards Optimal-Space Minimal Perfect Hashing Beyond Brute-Force | Symposium on Algorithm Engineering and Experiments (ALENEX'24) |
Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
| High Performance Construction of RecSplit Based Minimal Perfect Hash Functions | European Symposium on Algorithms (ESA'23) |
Dominik Bez, Florian Kurpicz, Hans-Peter Lehmann, Peter Sanders |
| SicHash – Small Irregular Cuckoo Tables for Perfect Hashing | Symposium on Algorithm Engineering and Experiments (ALENEX'23) |
Hans-Peter Lehmann, Peter Sanders, Stefan Walzer |
| Title | Type | Semester |
|---|---|---|
| Algorithmen I | Vorlesung / Übung (VÜ) | SS 2025 |
| Parallele Algorithmen | Vorlesung (V) | WS 24/25 |
| Seminar: Proofs from THE BOOK | Seminar (S) | SS 2024 |
| Randomisierte Algorithmik | Vorlesung / Übung (VÜ) | WS 23/24 |
| Karopapier-Rennen | Praxis der Softwareentwicklung | WS 23/24 |
| Seminar: Proofs from THE BOOK | Seminar | Summer term 2023 |
| Algorithms II | Lecture | Winter term 22/23 |
| Podcast-Synchronisations-Server | Praxis der Softwareentwicklung | WS 22/23 |
| Cloud Service für NP-schwere Probleme | Praxis der Softwareentwicklung | SS 2022 |
| Algorithmen II | Vorlesung (V) | WS 21/22 |
| Algorithm Engineering | Vorlesung (V) | SS 2021 |
| Title | Subject | Supervisor | Student |
|---|---|---|---|
| Wavelet Tree Construction on the GPU | Succinct Data Structures | Nikola Boban |
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| Engineering k-perfect hashing | Perfect Hashing | Sebastian Kirmayer |
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| Compacting Minimal Perfect Hashing using Symbiotic Random Search | Perfect Hashing | Jonatan Pascal Ziegler |
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| Cuckoo-PTHash: Exploring Cuckoo Hashing in the PTHash Framework | Perfect Hashing | Benedikt Waibel |
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| Accelerating Minimal Perfect Hash Function Construction using GPU Parallelization | Perfect Hashing | Stefan Hermann |
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| Engineering Succinct Predecessor Data Structures | Succinct Data Structures | Jan Benedikt Schwarz |
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| Compressed Bit Vectors with Rank and Select Support | Succinct Data Structures | Tobias Paweletz |
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| Perfect Hash Function Generation on the GPU | Perfect Hashing | Dominik Bez |