Strongly connected components: Difference between revisions

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== Definition ==
[[File:Scc.png|300px|thumb|right|Graph with marked strongly connected components]]
Let <math>G=(V,A)</math> be a [[Basic graph definitions|directed graph]]. Consider the following equivalence relation on the nodes: <math>v\in V</math> and <math>w\in V</math> are equivalent if, and only if, there is a path from <math>v</math> to <math>w</math> and a path from <math>w</math> to <math>v</math> in <math>G</math>. The equivalence classes are called the '''strongly connected components (SCC)''' of <math>G</math>.
== Input ==
== Input ==


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== Output ==
== Output ==


A set of sets of nodes. Each set of nodes contains exactly the nodes of one SCC. The correspndence between SCC and sets of nodes is one-to-one.
A set of sets of nodes. Each set of nodes contains exactly the nodes of one [[Basic graph definitions#Connectedness|SCC]]. The correspndence between the [[Basic graph definitions#Connectedness|SCC]] and these sets of nodes is one-to-one.


== Pseudocode ==  
== Pseudocode ==  

Revision as of 07:17, 3 November 2014

Input

A directed graph [math]\displaystyle{ G=(V,A) }[/math].

Output

A set of sets of nodes. Each set of nodes contains exactly the nodes of one SCC. The correspndence between the SCC and these sets of nodes is one-to-one.

Pseudocode

STRONGLY-CONNECTED-COMPONENTS(D)

STRONGLY-CONNECTED-COMPONENTS(D)
1 call DFS(D) to compute finishing times f[v] for each vertex vV
2 compute DT (w.r.t. step 3)
3 call DFS(DT), but in the main loop of DFS, consider the vertices in order of decreasing f[v] as computed in step 1
4 output the vertices of each tree in the DFS forest of step 3 as a separate strongly connected component

Known algorithms

  1. Kosaraju

Further information

STRONGLY-CONNECTED-COMPONENTS runs in linear time.