1 files changed, 236 insertions, 0 deletions
diff --git a/BJC-Utils2/src/main/java/bjc/utils/graph/Graph.java b/BJC-Utils2/src/main/java/bjc/utils/graph/Graph.java
new file mode 100644
index 0000000..69e42e4
--- /dev/null
+++ b/BJC-Utils2/src/main/java/bjc/utils/graph/Graph.java
@@ -0,0 +1,236 @@
+package bjc.utils.graph;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+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;
+
+/**
+ * A directed weighted graph, where the vertices have some arbitrary label
+ * 
+ * @author ben
+ *
+ * @param <T>
+ *            The label for vertices
+ */
+public class Graph<T> {
+
+	private final Map<T, Map<T, Integer>> graph;
+
+	/**
+	 * Create a new graph
+	 */
+	public Graph() {
+		graph = new HashMap<T, Map<T, Integer>>();
+	}
+
+	/**
+	 * 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
+	 */
+	public void addEdge(T source, T target, int distance) {
+		// Can't add edges with a null source or target
+		if (source == null) {
+			throw new NullPointerException("The vertex 1 cannot be null");
+		}
+		if (target == null) {
+			throw new NullPointerException("The vertex 2 cannot be null");
+		}
+
+		// Initialize adjacency list for vertices if necessary
+		if (!graph.containsKey(source)) {
+			graph.put(source, new HashMap<T, Integer>());
+		}
+		if (!graph.containsKey(target)) {
+			graph.put(target, new HashMap<T, Integer>());
+		}
+
+		// Add the edge to the graph
+		graph.get(source).put(target, distance);
+
+		// Uncomment this to make the graph undirected
+		// graph.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 bp
+	 *            The conditions an edge must match
+	 * @param bc
+	 *            The action to execute for matching edges
+	 */
+	public void forAllEdgesMatchingAt(T source, BiPredicate<T, Integer> bp,
+			BiConsumer<T, Integer> bc) {
+		getEdges(source).forEach((tgt, weight) -> {
+			if (bp.test(tgt, weight)) {
+				bc.accept(tgt, 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 Map<T, Integer> getEdges(T source) {
+		// Can't find edges for a null source
+		if (source == null) {
+			throw new NullPointerException("The source cannot be null.");
+		}
+
+		return Collections.unmodifiableMap(graph.get(source));
+	}
+
+	/**
+	 * Get the initial vertex of the graph
+	 * 
+	 * @return The initial vertex of the graph
+	 */
+	public T getInitial() {
+		return graph.keySet().iterator().next();
+	}
+
+	/**
+	 * Uses Prim's algorothm to calculate a MST for the graph. If the graph
+	 * is non-connected, this will lead to unpredictable results.
+	 * 
+	 * @param graph
+	 *            a connected graph.
+	 * @return a list of edges that constitute the MST
+	 */
+	public List<Edge<T>> getMinSpanTree() {
+		// Set of all of the currently available edges
+		Queue<Edge<T>> availEdges = new PriorityQueue<Edge<T>>(10,
+				(e1, e2) -> e1.getDistance() - e2.getDistance());
+
+		// The MST of the graph
+		List<Edge<T>> minEdges = new ArrayList<Edge<T>>();
+
+		// The set of all of the visited vertices.
+		Set<T> visited = new HashSet<T>();
+
+		// Start at the initial vertex and visit it
+		GenHolder<T> src = new GenHolder<>(getInitial());
+		visited.add(src.held);
+
+		// Make sure we visit all the nodes
+		while (visited.size() != getVertexCount()) {
+			// Grab all edges adjacent to the provided edge
+
+			forAllEdgesMatchingAt(src.held,
+					(tgt, weight) -> !visited.contains(tgt),
+					(tgt, weight) -> availEdges
+							.add(new Edge<T>(src.held, tgt, weight)));
+
+			// Get the edge with the minimum distance
+			Edge<T> minEdge = availEdges.poll();
+
+			// Only consider edges where we haven't visited the target of
+			// the edge
+			while (visited.contains(minEdge.getTarget())) {
+				minEdge = availEdges.poll();
+			}
+
+			// Add it to our MST
+			minEdges.add(minEdge);
+
+			// Advance to the next node
+			src.held = minEdge.getTarget();
+
+			// Visit this node
+			visited.add(src.held);
+		}
+
+		return minEdges;
+	}
+
+	public int getVertexCount() {
+		return graph.size();
+	}
+
+	/**
+	 * Get all of the vertices in this graph.
+	 * 
+	 * @return A unmodifiable set of all the vertices in the graph.
+	 */
+	public Set<T> getVertices() {
+		return Collections.unmodifiableSet(graph.keySet());
+	}
+
+	/**
+	 * 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(T source, T target) {
+		// Can't remove things w/ null vertices
+		if (source == null) {
+			throw new NullPointerException("The vertex 1 cannot be null");
+		}
+		if (target == null) {
+			throw new NullPointerException("The vertex 2 cannot be null");
+		}
+
+		// Can't remove if one vertice doesn't exists
+		if (!graph.containsKey(source)) {
+			throw new NoSuchElementException(
+					"vertex " + source + " does not exist.");
+		}
+		if (!graph.containsKey(target)) {
+			throw new NoSuchElementException(
+					"vertex " + target + " does not exist.");
+		}
+
+		graph.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<T> toMap() {
+		AdjacencyMap<T> aMap = new AdjacencyMap<>(graph.keySet());
+
+		graph.entrySet().forEach(src -> src.getValue().forEach((tgt,
+				weight) -> aMap.setWeight(src.getKey(), tgt, weight)));
+
+		return aMap;
+	}
+
+	public static <E> Graph<E> fromEdgeList(List<Edge<E>> edges) {
+		Graph<E> g = new Graph<>();
+
+		edges.forEach(edge -> g.addEdge(edge.getSource(), edge.getTarget(),
+				edge.getDistance()));
+
+		return g;
+	}
+}