| 1 | /* |
| 2 | * $Id: AdjacencyList.java 5865 2005-10-25 21:02:06Z dfs $ |
| 3 | * |
| 4 | * Copyright 2004 Daniel F. Savarese |
| 5 | * Copyright 2005 Savarese Software Research |
| 6 | * |
| 7 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | * you may not use this file except in compliance with the License. |
| 9 | * You may obtain a copy of the License at |
| 10 | * |
| 11 | * https://www.savarese.com/software/ApacheLicense-2.0 |
| 12 | * |
| 13 | * Unless required by applicable law or agreed to in writing, software |
| 14 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | * See the License for the specific language governing permissions and |
| 17 | * limitations under the License. |
| 18 | */ |
| 19 | |
| 20 | package com.savarese.algorithms.graph; |
| 21 | |
| 22 | import java.util.*; |
| 23 | |
| 24 | /** |
| 25 | * An AdjacencyList represents a graph by mapping a set of vertices to |
| 26 | * the set of {@link Edge edges} emanating from each vertex. |
| 27 | * |
| 28 | * @author <a href="https://www.savarese.com/">Daniel F. Savarese</a> |
| 29 | */ |
| 30 | |
| 31 | public class AdjacencyList<V, E extends Edge<V, ?>> |
| 32 | implements Graph<V, E> |
| 33 | { |
| 34 | |
| 35 | private HashMap<V, HashSet<E>> __map; |
| 36 | |
| 37 | /** |
| 38 | * Creates an empty adjacency list. |
| 39 | */ |
| 40 | public AdjacencyList() { |
| 41 | __map = new HashMap<V, HashSet<E>>(); |
| 42 | } |
| 43 | |
| 44 | |
| 45 | /** |
| 46 | * Adds a vertex to the graph if the vertex is not already |
| 47 | * contained in the graph. If it is not in the graph, an |
| 48 | * empty edge set is initialized. |
| 49 | * |
| 50 | * @param vertex The vertex to add. |
| 51 | * @return The set of edges emanating from the vertex. |
| 52 | */ |
| 53 | private Set<E> __addVertex(V vertex) { |
| 54 | HashSet<E> edges = __map.get(vertex); |
| 55 | |
| 56 | if(edges == null) { |
| 57 | edges = new HashSet<E>(); |
| 58 | __map.put(vertex, edges); |
| 59 | } |
| 60 | |
| 61 | return edges; |
| 62 | } |
| 63 | |
| 64 | |
| 65 | public void add(E edge) { |
| 66 | __addVertex(edge.getSource()).add(edge); |
| 67 | addVertex(edge.getDestination()); |
| 68 | } |
| 69 | |
| 70 | |
| 71 | public void addVertex(V vertex) { |
| 72 | __addVertex(vertex); |
| 73 | } |
| 74 | |
| 75 | |
| 76 | public void clear() { |
| 77 | __map.clear(); |
| 78 | } |
| 79 | |
| 80 | |
| 81 | public Set<E> edgeSet(V v) { |
| 82 | Set<E> edges = __map.get(v); |
| 83 | |
| 84 | if(edges == null) |
| 85 | return null; |
| 86 | |
| 87 | return edges; |
| 88 | } |
| 89 | |
| 90 | |
| 91 | public int size() { |
| 92 | return __map.size(); |
| 93 | } |
| 94 | |
| 95 | |
| 96 | public Set<V> vertexSet() { |
| 97 | return __map.keySet(); |
| 98 | } |
| 99 | } |
