The lca package

[Tags: bsd3, library]

This package provides a reference implementation of my skew binary random access algorithm for performing an online lowest common ancestor search (and online level ancestor search) in logarithmic time without preprocessing. This improves the previous known asymptotic bound for both of these problems from O(h) to O(log h), where h is the height of the tree. Mostly importantly this bound is completely independent of the width or overall size of the tree, enabling you to calculate lowest common ancestors in a distributed fashion with good locality.

While offline algorithms exist for both of these algorithms that that provide O(1) query time, they all require at least O(n) preprocessing, where n is the size of the entire tree, and so are less suitable for LCA search in areas such as revision control where the tree is constantly updated, or distributed computing where the tree may be too large to fit in any one computer's memory.

Slides are available from


Versions0.1,, 0.2, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.3
Dependenciesbase (==4.*)
CopyrightCopyright (C) 2011-2015 Edward A. Kmett
AuthorEdward A. Kmett
MaintainerEdward A. Kmett <>
CategoryAlgorithms, Data Structures
Home page
Bug tracker
Source repositoryhead: git clone git://
UploadedSun Mar 8 10:04:00 UTC 2015 by EdwardKmett
DistributionsLTSHaskell:0.3, NixOS:0.3, Stackage:0.3
Downloads1220 total (49 in last 30 days)
StatusDocs available [build log]
Last success reported on 2015-03-08 [all 1 reports]




Maintainers' corner

For package maintainers and hackage trustees