74 lines
2.6 KiB
Java
74 lines
2.6 KiB
Java
package com.jwetherell.algorithms.graph;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import com.jwetherell.algorithms.data_structures.Graph;
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import com.jwetherell.algorithms.data_structures.Graph.Edge;
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import com.jwetherell.algorithms.data_structures.Graph.Vertex;
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/**
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* In graph theory, a connected component (or just component) of an undirected graph is a subgraph in which any two vertices are connected to each
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* other by paths, and which is connected to no additional vertices in the supergraph. A vertex with no incident edges is itself a connected
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* component. A graph that is itself connected has exactly one connected component, consisting of the whole graph.
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*
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* http://en.wikipedia.org/wiki/Connected_component_(graph_theory)
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*
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* @author Justin Wetherell <phishman3579@gmail.com>
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*/
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public class ConnectedComponents {
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private ConnectedComponents() { }
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/**
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* Finds the connected components subsets of the Graph.
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*
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* @param g Graph to find connected components.
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* @return List of connected components in the Graph.
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*/
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public static final <T extends Comparable<T>> List<List<Vertex<T>>> getConnectedComponents(Graph<T> graph) {
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if (graph == null)
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throw new IllegalArgumentException("Graph is NULL.");
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if (graph.getType() != Graph.TYPE.DIRECTED)
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throw new IllegalArgumentException("Cannot perform a connected components search on a non-directed graph. graph type = "+graph.getType());
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final Map<Vertex<T>,Integer> map = new HashMap<Vertex<T>,Integer>();
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final List<List<Vertex<T>>> list = new ArrayList<List<Vertex<T>>>();
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int c = 0;
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for (Vertex<T> v : graph.getVertices())
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if (map.get(v) == null)
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visit(map, list, v, c++);
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return list;
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}
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private static final <T extends Comparable<T>> void visit(Map<Vertex<T>,Integer> map, List<List<Vertex<T>>> list, Vertex<T> v, int c) {
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map.put(v, c);
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List<Vertex<T>> r = null;
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if (c == list.size()) {
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r = new ArrayList<Vertex<T>>();
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list.add(r);
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} else {
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r = list.get(c);
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}
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r.add(v);
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if (v.getEdges().size() > 0) {
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boolean found = false;
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for (Edge<T> e : v.getEdges()) {
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final Vertex<T> to = e.getToVertex();
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if (map.get(to) == null) {
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visit(map, list, to, c);
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found = true;
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}
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if (found)
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break;
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}
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}
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}
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}
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