Esempio n. 1
0
        public static void Main(string[] args)
        {           
            #region create graph: https://en.wikipedia.org/wiki/Prim%27s_algorithm
            Graph graph = new Graph();
            graph.AddEdges(0, 1, 2);
            graph.AddEdges(0, 3, 1);
            graph.AddEdges(1, 3, 2);
            graph.AddEdges(2, 3, 3);           
            #endregion

            foreach (Edge e in PrimsAlgorithm(graph))
            {
                Console.WriteLine(String.Format("Edge ({0}, {1})", e.vertexU, e.vertexV));                
            }
            
            Console.WriteLine("Press any key...");
            Console.ReadKey();
        }
Esempio n. 2
0
        public static List<Edge> PrimsAlgorithm(Graph graph)
        {
            List<Edge> minSpanningTree = new List<Edge>();
            List<Edge> unselectedEdges = new List<Edge>(graph.Edges);
            List<int> unselectedVertices = new List<int>(graph.Vertices);
            List<int> selectedVertices = new List<int>();

            // random selection of vertex
            selectedVertices.Add(new Random().Next(0, graph.Vertices.Count()));
            unselectedVertices.RemoveAt(selectedVertices[0]);

            while (unselectedVertices.Count > 0)
            {
                int indexMinEdge = -1;

                // search the minimum-weight edge
                for (int i = 0; i < unselectedEdges.Count; i++)
                {
                    if ((selectedVertices.IndexOf(unselectedEdges[i].vertexU) != -1) && (unselectedVertices.IndexOf(unselectedEdges[i].vertexV) != -1) ||
                        (selectedVertices.IndexOf(unselectedEdges[i].vertexV) != -1) && (unselectedVertices.IndexOf(unselectedEdges[i].vertexU) != -1))
                    {
                        indexMinEdge = indexMinEdge == -1 ? i : (unselectedEdges[i].weight < unselectedEdges[indexMinEdge].weight ? i : indexMinEdge);                        
                    }
                }

                // add a new vertex (U or V) to the selected list and remove from list unselected
                if (selectedVertices.IndexOf(unselectedEdges[indexMinEdge].vertexU) != -1)
                {
                    selectedVertices.Add(unselectedEdges[indexMinEdge].vertexV);
                    unselectedVertices.Remove(unselectedEdges[indexMinEdge].vertexV);
                }
                else
                {
                    selectedVertices.Add(unselectedEdges[indexMinEdge].vertexU);
                    unselectedVertices.Remove(unselectedEdges[indexMinEdge].vertexU);
                }

                // add a new edge to the tree and delete from the list of unselected
                minSpanningTree.Add(unselectedEdges[indexMinEdge]);
                unselectedEdges.RemoveAt(indexMinEdge);
            }

            return minSpanningTree;
        }