Пример #1
0
        /// <summary>
        /// Get shortest distance to target.
        /// </summary>
        public ShortestPathResult <T, W> FindShortestPath(IGraph <T> graph, T source, T destination)
        {
            //regular argument checks
            if (graph?.GetVertex(source) == null || graph.GetVertex(destination) == null)
            {
                throw new ArgumentException();
            }

            if (this.@operator == null)
            {
                throw new ArgumentException("Provide an operator implementation for generic type W during initialization.");
            }

            if (!graph.IsWeightedGraph)
            {
                if ([email protected]() != typeof(int))
                {
                    throw new ArgumentException("Edges of unweighted graphs are assigned an imaginary weight of one (1)." +
                                                "Provide an appropriate IShortestPathOperators<int> operator implementation during initialization.");
                }
            }

            //track progress for distance to each Vertex from source
            var progress = new Dictionary <T, W>();

            //trace our current path by mapping current vertex to its Parent
            var parentMap = new Dictionary <T, T>();

            //min heap to pick next closest vertex
            var minHeap = new FibonacciHeap <MinHeapWrap <T, W> >();
            //keep references of heap Node for decrement key operation
            var heapMapping = new Dictionary <T, MinHeapWrap <T, W> >();

            //add vertices to min heap and progress map
            foreach (var vertex in graph.VerticesAsEnumberable)
            {
                //init parent
                parentMap.Add(vertex.Key, default(T));

                //init to max value
                progress.Add(vertex.Key, @operator.MaxValue);

                if (vertex.Key.Equals(source))
                {
                    continue;
                }
            }

            //start from source vertex as current
            var current = new MinHeapWrap <T, W>()
            {
                Distance = @operator.DefaultValue,
                Vertex   = source
            };

            minHeap.Insert(current);
            heapMapping.Add(current.Vertex, current);

            //until heap is empty
            while (minHeap.Count > 0)
            {
                //next min vertex to visit
                current = minHeap.Extract();
                heapMapping.Remove(current.Vertex);

                //no path exists, so return max value
                if (current.Distance.Equals(@operator.MaxValue))
                {
                    return(new ShortestPathResult <T, W>(null, @operator.MaxValue));
                }

                //visit neighbours of current
                foreach (var neighbour in graph.GetVertex(current.Vertex).Edges.Where(x => !x.TargetVertexKey.Equals(source)))
                {
                    //new distance to neighbour
                    var newDistance = @operator.Sum(current.Distance,
                                                    graph.GetVertex(current.Vertex).GetEdge(neighbour.TargetVertex).Weight <W>());

                    //current distance to neighbour
                    var existingDistance = progress[neighbour.TargetVertexKey];

                    //update distance if new is better
                    if (newDistance.CompareTo(existingDistance) < 0)
                    {
                        progress[neighbour.TargetVertexKey] = newDistance;

                        if (!heapMapping.ContainsKey(neighbour.TargetVertexKey))
                        {
                            var wrap = new MinHeapWrap <T, W>()
                            {
                                Distance = newDistance, Vertex = neighbour.TargetVertexKey
                            };
                            minHeap.Insert(wrap);
                            heapMapping.Add(neighbour.TargetVertexKey, wrap);
                        }
                        else
                        {
                            //decrement distance to neighbour in heap
                            var decremented = new MinHeapWrap <T, W>()
                            {
                                Distance = newDistance, Vertex = neighbour.TargetVertexKey
                            };
                            minHeap.UpdateKey(heapMapping[neighbour.TargetVertexKey], decremented);
                            heapMapping[neighbour.TargetVertexKey] = decremented;
                        }

                        //trace parent
                        parentMap[neighbour.TargetVertexKey] = current.Vertex;
                    }
                }
            }

            return(tracePath(graph, parentMap, source, destination));
        }
        /// <summary>
        /// Get shortest distance to target.
        /// </summary>
        public ShortestPathResult <T, W> FindShortestPath(WeightedDiGraph <T, W> graph, T source, T destination)
        {
            //regular argument checks
            if (graph?.FindVertex(source) == null || graph.FindVertex(destination) == null)
            {
                throw new ArgumentException();
            }

            //track progress for distance to each Vertex from source
            var progress = new Dictionary <T, W>();

            //trace our current path by mapping current vertex to its Parent
            var parentMap = new Dictionary <T, T>();

            //min heap to pick next closest vertex
            var minHeap = new FibornacciHeap <MinHeapWrap <T, W> >();
            //keep references of heap Node for decrement key operation
            var heapMapping = new Dictionary <T, MinHeapWrap <T, W> >();

            //add vertices to min heap and progress map
            foreach (var vertex in graph.Vertices)
            {
                //init parent
                parentMap.Add(vertex.Key, default(T));

                //init to max value
                progress.Add(vertex.Key, operators.MaxValue);

                if (vertex.Key.Equals(source))
                {
                    continue;
                }
            }

            //start from source vertex as current
            var current = new MinHeapWrap <T, W>()
            {
                Distance = operators.DefaultValue,
                Vertex   = source
            };

            minHeap.Insert(current);
            heapMapping.Add(current.Vertex, current);

            //until heap is empty
            while (minHeap.Count > 0)
            {
                //next min vertex to visit
                current = minHeap.Extract();
                heapMapping.Remove(current.Vertex);

                //no path exists, so return max value
                if (current.Distance.Equals(operators.MaxValue))
                {
                    return(new ShortestPathResult <T, W>(null, operators.MaxValue));
                }

                //visit neighbours of current
                foreach (var neighbour in graph.Vertices[current.Vertex].OutEdges.Where(x => !x.Key.Value.Equals(source)))
                {
                    //new distance to neighbour
                    var newDistance = operators.Sum(current.Distance,
                                                    graph.Vertices[current.Vertex].OutEdges[neighbour.Key]);

                    //current distance to neighbour
                    var existingDistance = progress[neighbour.Key.Value];

                    //update distance if new is better
                    if (newDistance.CompareTo(existingDistance) < 0)
                    {
                        progress[neighbour.Key.Value] = newDistance;

                        if (!heapMapping.ContainsKey(neighbour.Key.Value))
                        {
                            var wrap = new MinHeapWrap <T, W>()
                            {
                                Distance = newDistance, Vertex = neighbour.Key.Value
                            };
                            minHeap.Insert(wrap);
                            heapMapping.Add(neighbour.Key.Value, wrap);
                        }
                        else
                        {
                            //decrement distance to neighbour in heap
                            var decremented = new MinHeapWrap <T, W>()
                            {
                                Distance = newDistance, Vertex = neighbour.Key.Value
                            };
                            minHeap.UpdateKey(heapMapping[neighbour.Key.Value], decremented);
                            heapMapping[neighbour.Key.Value] = decremented;
                        }

                        //trace parent
                        parentMap[neighbour.Key.Value] = current.Vertex;
                    }
                }
            }

            return(tracePath(graph, parentMap, source, destination));
        }
Пример #3
0
        /// <summary>
        /// Get shortest distance to target
        /// </summary>
        /// <param name="graph"></param>
        /// <param name="source"></param>
        /// <param name="destination"></param>
        /// <returns></returns>
        public ShortestPathResult <T, W> GetShortestPath(WeightedDiGraph <T, W> graph, T source, T destination)
        {
            //regular argument checks
            if (graph?.FindVertex(source) == null || graph.FindVertex(destination) == null)
            {
                throw new ArgumentException();
            }

            //track progress for distance to each Vertex from source
            var progress = new System.Collections.Generic.Dictionary <T, W>();

            //trace our current path by mapping current vertex to its Parent
            var parentMap = new System.Collections.Generic.Dictionary <T, T>();

            //min heap to pick next closest vertex
            var minHeap = new FibornacciMinHeap <MinHeapWrap <T, W> >();
            //keep references of heap Node for decrement key operation
            var heapMapping = new System.Collections.Generic.Dictionary <T, FibornacciHeapNode <MinHeapWrap <T, W> > >();

            //add vertices to min heap and progress map
            foreach (var vertex in graph.Vertices)
            {
                //init parent
                parentMap.Add(vertex.Key, default(T));

                //init to max value
                progress.Add(vertex.Key, operators.MaxValue);

                if (vertex.Key.Equals(source))
                {
                    continue;
                }

                //construct heap for all vertices with Max Distance as default
                var wrap = new MinHeapWrap <T, W>()
                {
                    Distance = operators.MaxValue,
                    Target   = vertex.Key
                };

                var heapNode = minHeap.Insert(wrap);
                heapMapping.Add(vertex.Key, heapNode);
            }

            //start from source vertex as current
            var current = new MinHeapWrap <T, W>()
            {
                Distance = operators.DefaultValue,
                Target   = source
            };

            //until heap is empty
            while (minHeap.Count > 0)
            {
                //no path exists, so return max value
                if (current.Distance.Equals(operators.MaxValue))
                {
                    return(new ShortestPathResult <T, W>(null, operators.MaxValue));
                }

                //visit neighbours of current
                foreach (var neighbour in graph.Vertices[current.Target].OutEdges)
                {
                    //new distance to neighbour
                    var newDistance = operators.Sum(current.Distance,
                                                    graph.Vertices[current.Target].OutEdges[neighbour.Key]);

                    //current distance to neighbour
                    var existingDistance = progress[neighbour.Key.Value];

                    //update distance if new is better
                    if (newDistance.CompareTo(existingDistance) < 0)
                    {
                        progress[neighbour.Key.Value] = newDistance;
                        heapMapping[neighbour.Key.Value].Value.Distance = newDistance;

                        //decrement distance to neighbour in heap
                        minHeap.DecrementKey(heapMapping[neighbour.Key.Value]);

                        //trace parent
                        parentMap[neighbour.Key.Value] = current.Target;
                    }
                }

                //next min vertex to visit
                current = minHeap.ExtractMin();
            }

            return(tracePath(graph, parentMap, source, destination));
        }
Пример #4
0
 public int CompareTo(MinHeapWrap <T, W> other)
 {
     return(Distance.CompareTo(other.Distance));
 }