implemented Prim

mySpanningTree.java

@@ -37,7 +37,60 @@ public class mySpanningTree {
 	}
 
 	public static AsSubgraph<Integer, DefaultWeightedEdge> primAlgorithm(AsSubgraph<Integer, DefaultWeightedEdge> tree, Graph<Integer, DefaultWeightedEdge> graph) {
-		// Input: tree -> 
+		// begin
+		// Set F = 0 -> Schon geschehen
+		Set<Integer> V = graph.vertexSet();
+		Set<DefaultWeightedEdge> E = graph.edgeSet();
+		
+		// choose w in V and define X = {w}
+		int start_vertex = 1; // <- Wird bei Prim ja eigentlich beliebig gewählt, nicht?
+		Set<Integer> X = new HashSet<Integer>();
+		X.add(start_vertex);
+		
+		// while X != V do
+		while (X.size() != V.size()) {
+			
+			// choose an edge {u,v} in E of smallest possible weight with u € X and v € V \ X
+			DefaultWeightedEdge uv = new DefaultWeightedEdge(); 				// edge with smallest_possible weight
+			double uv_weight = Double.MAX_VALUE;
+			
+			Iterator<Integer> X_it = X.iterator(); 	// iterate over set vertices
+			while (X_it.hasNext()) {
+				int u = X_it.next();
+				Set<DefaultWeightedEdge> outgoing_edges = graph.outgoingEdgesOf(u);		// get outgoing edges of set vertex
+				
+				Iterator<DefaultWeightedEdge> outgoing_it = outgoing_edges.iterator();	// iterate over outgoing edges
+				while (outgoing_it.hasNext()) {
+					DefaultWeightedEdge e = outgoing_it.next();
+					int target = graph.getEdgeTarget(e);
+					if (target == u) {
+						target = graph.getEdgeSource(e);
+					}
+					if (!X.contains(target)) { 				// check that edge target vertex isn't already set
+						double weight = graph.getEdgeWeight(e);
+						if (weight < uv_weight) {
+							uv = e;
+							uv_weight = weight;
+						}
+					}
+				}
+			}
+			
+			// put {u,v} in F
+			int source = graph.getEdgeSource(uv);
+			int target = graph.getEdgeTarget(uv);
+			
+			if (X.contains(target)) {
+				source = target;
+				target = graph.getEdgeSource(uv);
+			}
+			
+			tree.addEdge(source, target);
+			tree.setEdgeWeight(source, target, uv_weight);
+			
+			// put v in X
+			X.add(target);
+		}
 
 		return tree;
 	}