A Clojure implementation of persistent disjoint-set forests using Tarjan's union-find algorithm.
com.github.jordanlewis/data.union-find {:git/tag "1.0.0" :sha "0e8a06f"}
This is not currently released on Clojars. If someone needs that, please put in a ticket and it can be done.
This library is stable and I do not currently anticipate any changes.
Make a new union-find data structure containing its arguments as singleton sets:
(use 'jordanlewis.data.union-find)
(def uf (union-find 1 2 3 4 5))
uf
;; => {5 [5], 4 [4], 3 [3], 2 [2], 1 [1]}
Add a new element as a singleton set with conj or cons:
(conj uf 8)
;; => {8 [8], 5 [5], 4 [4], 2 [3 2], 1 [1]}
Union two sets:
(def uf (union uf 2 3))
uf
;; => {5 [5], 4 [4], 2 [3 2], 1 [1]}
Look up the canonical element for an element:
(get-canonical uf 3)
;; => [{5 [5], 4 [4], 2 [3 2], 1 [1]} 2]
Union find also supports being used as a transient editable collection, which can improve performance in some scenarios:
(-> (transient uf)
(union! 2 5)
persistent!)
Getting the canonical element of a set can change the internals of the data structure, due to an optimization called path compression. Therefore, get-canonical returns two objects: the updated data structure, and the requested canonical element.
Getting the count of a union-find data structure returns the number of connected components, not the number of elements. count is a constant-time operation.
(count uf) ;; => 4
;; 4 connected components, but 5 elements
Treating a union-find data structure as a seq similiarly returns only the canonical elements of the data structure, not all of the elements:
(seq uf) ;; => (5 4 2 1)
;; doesn't include 3, which is a non-canonical element
union-find also implements ILookup and IFn as canonical element lookups, so you can use get on it or apply it to an element like you would with a vector or a map. Using it this way doesn't perform the path compression optimization, and just returns the canonical element.
(uf 3) ;; => 2
(get uf 3) ;; => 2
(uf 10) ;; => nil
(uf 10 :not-found) ;; => :not-found
Copyright © 2012-2022 Jordan Lewis and Darrick Wiebe
Distributed under the Eclipse Public License, the same as Clojure.