UnionFind 1.0.1

UnionFind 1.0.1

TestsTested
LangLanguage Obj-CObjective C
License Custom
ReleasedLast Release Dec 2014

Maintained by Unclaimed.


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UnionFind 1.0.1

  • By
  • Craig Gidney

UnionFind for Objective-C

This is a tiny library implementing a union find / disjoint set data structure, featuring:

  • Nodes: The only type is UFDisjointSetNode. A UFDisjointSetNode is a member of some implicit set of nodes. At any given time, the set is represented by some single specific node among its members. Sets never partially overlap; they are either the same set or have no nodes in common.
  • Union-ing: Use unionWith: to merge the sets two UFDisjointSetNodes are members of into a single set.
  • Find-ing: Use isInSameSetAs: to determine if two UFDisjointSetNodes are in the same set. Use currentRepresentative to get the current node representing the set the receiving node is in. Nodes are in the same set when they have the same representative.

Installation

Method #1: CocoaPods

  1. In your Podfile, add pod 'UnionFind'
  2. Consider versioning, like: pod 'UnionFind', '~> 1.0'
  3. Run pod install from a terminal in your project directory
  4. #import "UnionFind.h" wherever you want to access the library's types or methods

Method #2: Manual

  1. Download one of the releases, or clone the repo
  2. Copy the source files from the src/ folder into your project
  3. Have ARC enabled
  4. #import "UnionFind.h" wherever you want to access the library's types or methods

Algorithm

The algorithm is sourced from wikipedia's disjoint set data structure article. Operations take amortized nearly constant time.

Usage

In the class that you want to union together, add a field of type UFDisjointSetNode. Initialize the node, either eagerly when the class is constructed or lazily just before it is needed, then perform operations on it.

For example, suppose we have a FancyGraphNode to which edges can be added but not removed. We want to track if nodes are in the same connected component. We can:

  1. Add the field @private UFDisjointSetNode* _ccNode to FancyGraphNode
  2. Initialize the field in the init function: _ccNode = [UFDisjointSetNode new].
  3. When adding an edge, call [edge.Node1._ccNode unionWith:edge.Node2._ccNode].
  4. To determine if two nodes are in the same component, evaluate [node1._ccNode isInSameSetAs:node2._ccNode].

An example application is discussed in this blog post about incremental cycle detection.