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Faster Path Queries in Colored Trees via Sparse Matrix Multiplication and Min-Plus Product

Authors Younan Gao, Meng He

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Younan Gao
  • Faculty of Computer Science, Dalhousie University, Halifax, Canada
Meng He
  • Faculty of Computer Science, Dalhousie University, Halifax, Canada

Funding

This work was supported by NSERC of Canada.

Acknowledgements

The authors would like to thank the anonymous reviewers for their valueable comments and suggestions.

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Younan Gao and Meng He. Faster Path Queries in Colored Trees via Sparse Matrix Multiplication and Min-Plus Product. In 30th Annual European Symposium on Algorithms (ESA 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 244, pp. 59:1-59:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022) https://doi.org/10.4230/LIPIcs.ESA.2022.59

Abstract

Let T be an ordinal tree on n nodes in which each node is assigned a color. We consider the batched colored path counting problem and the batched path mode/least frequent element query problem, in which given n query paths, each identified by a pair of nodes in T, one is asked to answer queries of the following forms: How many distinct colors are there on each query path (i.e. the colored path counting problem); what is the color on each query path that occurs at least/most as frequently as any other colors (i.e. the path mode/least frequent element query problem). By reducing the batched colored path counting problem to sparse matrix multiplication, we design a solution that answers n colored path counting queries in Õ(n^{2ω/(ω+1)}) = O(n^1.40704) time in total, while we reduce batched path mode/least frequent element query to the min-plus-query-witness problem so that we can answer a batch of n queries in Õ(n^{{24+2ω}/{17+ω}}) = O(n^1.483814) time. Previously, both problems could only be solved in Õ(n^1.5) time. 
Based on similar techniques, we design a dynamic colored path counting structure supporting both queries and updates in Õ(n^{{ω+1}/{ω+3}}) = O(n^0.627759) time, while our dynamic path mode/least frequent element query structures support each operation in Õ(n^{{16+ω(1,2,1)}/{26+ω(1,2,1)}}) = O(n^0.658139) time, where ω(1, 2, 1) denotes the minimum value such that the product of an n × n² matrix and an n² × n matrix can be computed in O(n^{ω(1, 2, 1)+ε}) time for any constant ε > 0. We also solve batched range mode/least frequent element query problems over arrays in Õ(n^{{18+2ω}/{13+ω}}) = O(n^1.479603) time. Both problems can be viewed as special cases of these batched path queries, and previously, the fastest algorithm for batched range mode queries and batched range least frequent element queries use O(n^1.4805) and Õ(n^1.5) time, respectively.

Subject Classification

ACM Subject Classification
  • Theory of computation → Data structures design and analysis
  • Information systems → Data structures
Keywords
  • min-plus product
  • range mode queries
  • range least frequent queries
  • path queries
  • colored path counting
  • path mode queries
  • path least frequent queries

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