From c82e3b3b2de0633317ec8fc85925e91422820597 Mon Sep 17 00:00:00 2001 From: "Benjamin J. Culkin" Date: Sun, 8 Oct 2017 22:39:59 -0300 Subject: Start splitting into maven modules --- base/src/main/java/bjc/utils/graph/Graph.java | 267 ++++++++++++++++++++++++++ 1 file changed, 267 insertions(+) create mode 100644 base/src/main/java/bjc/utils/graph/Graph.java (limited to 'base/src/main/java/bjc/utils/graph/Graph.java') diff --git a/base/src/main/java/bjc/utils/graph/Graph.java b/base/src/main/java/bjc/utils/graph/Graph.java new file mode 100644 index 0000000..280a7f5 --- /dev/null +++ b/base/src/main/java/bjc/utils/graph/Graph.java @@ -0,0 +1,267 @@ +package bjc.utils.graph; + +import java.util.ArrayList; +import java.util.HashSet; +import java.util.List; +import java.util.NoSuchElementException; +import java.util.PriorityQueue; +import java.util.Queue; +import java.util.Set; +import java.util.function.BiConsumer; +import java.util.function.BiPredicate; + +import bjc.utils.data.IHolder; +import bjc.utils.data.Identity; +import bjc.utils.funcdata.FunctionalMap; +import bjc.utils.funcdata.IList; +import bjc.utils.funcdata.IMap; + +/** + * A directed weighted graph, where the vertices have some arbitrary label + * + * @author ben + * + * @param + * The label for vertices + */ +public class Graph { + /** + * Create a graph from a list of edges + * + * @param + * The type of data stored in the edges + * + * @param edges + * The list of edges to build from + * @return A graph built from the provided edge-list + */ + public static Graph fromEdgeList(final List> edges) { + final Graph g = new Graph<>(); + + edges.forEach(edge -> { + g.addEdge(edge.getSource(), edge.getTarget(), edge.getDistance(), true); + }); + + return g; + } + + /** + * The backing representation of the graph + */ + private final IMap> backing; + + /** + * Create a new graph + */ + public Graph() { + backing = new FunctionalMap<>(); + } + + /** + * Add a edge to the graph + * + * @param source + * The source vertex for this edge + * @param target + * The target vertex for this edge + * @param distance + * The distance from the source vertex to the target + * vertex + * @param directed + * Whether or not + */ + public void addEdge(final T source, final T target, final int distance, final boolean directed) { + // Can't add edges with a null source or target + if (source == null) + throw new NullPointerException("The source vertex cannot be null"); + else if (target == null) throw new NullPointerException("The target vertex cannot be null"); + + // Initialize adjacency list for vertices if necessary + if (!backing.containsKey(source)) { + backing.put(source, new FunctionalMap()); + } + + // Add the edge to the graph + backing.get(source).put(target, distance); + + // Handle possible directed edges + if (!directed) { + if (!backing.containsKey(target)) { + backing.put(target, new FunctionalMap()); + } + + backing.get(target).put(source, distance); + } + } + + /** + * Execute an action for all edges of a specific vertex matching + * conditions + * + * @param source + * The vertex to test edges for + * @param matcher + * The conditions an edge must match + * @param action + * The action to execute for matching edges + */ + public void forAllEdgesMatchingAt(final T source, final BiPredicate matcher, + final BiConsumer action) { + if (matcher == null) + throw new NullPointerException("Matcher must not be null"); + else if (action == null) throw new NullPointerException("Action must not be null"); + + getEdges(source).forEach((target, weight) -> { + if (matcher.test(target, weight)) { + action.accept(target, weight); + } + }); + } + + /** + * Get all the edges that begin at a particular source vertex + * + * @param source + * The vertex to use as a source + * @return All of the edges with the specified vertex as a source + */ + public IMap getEdges(final T source) { + // Can't find edges for a null source + if (source == null) + throw new NullPointerException("The source cannot be null."); + else if (!backing.containsKey(source)) + throw new IllegalArgumentException("Vertex " + source + " is not in graph"); + + return backing.get(source); + } + + /** + * Get the initial vertex of the graph + * + * @return The initial vertex of the graph + */ + public T getInitial() { + return backing.keyList().first(); + } + + /** + * Uses Prim's algorothm to calculate a MST for the graph. + * + * If the graph is non-connected, this will lead to unpredictable + * results. + * + * @return a list of edges that constitute the MST + */ + public List> getMinimumSpanningTree() { + // Set of all of the currently available edges + final Queue> available = new PriorityQueue<>(10, + (left, right) -> left.getDistance() - right.getDistance()); + + // The MST of the graph + final List> minimums = new ArrayList<>(); + + // The set of all of the visited vertices. + final Set visited = new HashSet<>(); + + // Start at the initial vertex and visit it + final IHolder source = new Identity<>(getInitial()); + + visited.add(source.getValue()); + + // Make sure we visit all the nodes + while (visited.size() != getVertexCount()) { + // Grab all edges adjacent to the provided edge + + forAllEdgesMatchingAt(source.getValue(), (target, weight) -> { + return !visited.contains(target); + }, (target, weight) -> { + final T vert = source.unwrap(vertex -> vertex); + + available.add(new Edge<>(vert, target, weight)); + }); + + // Get the edge with the minimum distance + final IHolder> minimum = new Identity<>(available.poll()); + + // Only consider edges where we haven't visited the + // target of + // the edge + while (visited.contains(minimum.getValue().getTarget())) { + minimum.transform((edge) -> available.poll()); + } + + // Add it to our MST + minimums.add(minimum.getValue()); + + // Advance to the next node + source.transform((vertex) -> minimum.unwrap(edge -> edge.getTarget())); + + // Visit this node + visited.add(source.getValue()); + } + + return minimums; + } + + /** + * Get the count of the vertices in this graph + * + * @return A count of the vertices in this graph + */ + public int getVertexCount() { + return backing.size(); + } + + /** + * Get all of the vertices in this graph. + * + * @return A unmodifiable set of all the vertices in the graph. + */ + public IList getVertices() { + return backing.keyList(); + } + + /** + * Remove the edge starting at the source and ending at the target + * + * @param source + * The source vertex for the edge + * @param target + * The target vertex for the edge + */ + public void removeEdge(final T source, final T target) { + // Can't remove things w/ null vertices + if (source == null) + throw new NullPointerException("The source vertex cannot be null"); + else if (target == null) throw new NullPointerException("The target vertex cannot be null"); + + // Can't remove if one vertice doesn't exists + if (!backing.containsKey(source)) + throw new NoSuchElementException("vertex " + source + " does not exist."); + + if (!backing.containsKey(target)) + throw new NoSuchElementException("vertex " + target + " does not exist."); + + backing.get(source).remove(target); + + // Uncomment this to turn the graph undirected + // graph.get(target).remove(source); + } + + /** + * Convert a graph into a adjacency map/matrix + * + * @return A adjacency map representing this graph + */ + public AdjacencyMap toAdjacencyMap() { + final AdjacencyMap adjacency = new AdjacencyMap<>(backing.keyList()); + + backing.forEach((sourceKey, sourceValue) -> { + sourceValue.forEach((targetKey, targetValue) -> { + adjacency.setWeight(sourceKey, targetKey, targetValue); + }); + }); + + return adjacency; + } +} -- cgit v1.2.3