io.stargate.graphql.schema.graphqlfirst.util

Class DirectedGraph<VertexT>

java.lang.Object

io.stargate.graphql.schema.graphqlfirst.util.DirectedGraph<VertexT>

@NotThreadSafe
public class DirectedGraph<VertexT>
extends Object

A basic directed graph implementation to perform topological sorts.

This class is not a general-purpose graph implementation: it is only intended for clients that will build a graph, sort it, and then immediately throw it away. In particular, once topologicalSort() has been invoked, it is not possible to add vertices or sort again.

Constructor Summary

Constructors

Constructor and Description
DirectedGraph(Collection<VertexT> vertices)

Method Summary

Modifier and Type	Method and Description
void	addEdge(VertexT from, VertexT to)
List<VertexT>	topologicalSort() Performs a topological sort of the graph: for every directed edge from->to, from will come before to in the resulting list.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DirectedGraph

public DirectedGraph(Collection<VertexT> vertices)

Method Detail

addEdge

public void addEdge(VertexT from,
                    VertexT to)

Throws:

IllegalStateException - if topologicalSort() was invoked before

IllegalArgumentException - if from or to is not part of the vertices passed to the constructor

topologicalSort

public List<VertexT> topologicalSort()

Performs a topological sort of the graph: for every directed edge from->to, from will come before to in the resulting list.

Implementation note: this is based on Kahn's algorithm, the running time is linear in the number of nodes plus the number of edges.

Throws:

IllegalStateException - if this method was already invoked on this graph before

IllegalArgumentException - if the graph has a cycle