| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.axiom.core.util; |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.HashSet; |
| import java.util.List; |
| import java.util.Set; |
| |
| /** |
| * Implements topological sorting. |
| */ |
| public final class TopologicalSort { |
| private TopologicalSort() {} |
| |
| private static <T> void visit(Collection<T> vertices, EdgeRelation<? super T> edgeRelation, List<T> result, Set<T> visited, T vertex) { |
| if (visited.add(vertex)) { |
| for (T vertex2 : vertices) { |
| if (vertex2 != vertex && edgeRelation.isEdge(vertex, vertex2)) { |
| visit(vertices, edgeRelation, result, visited, vertex2); |
| } |
| } |
| result.add(vertex); |
| } |
| } |
| |
| /** |
| * Apply topological ordering to a given collection. |
| * |
| * @param <T> |
| * the vertex type |
| * @param vertices |
| * the vertices of the directed acyclic graph |
| * @param edgeRelation |
| * the relation defining the edges of the graph |
| * @return the topologically sorted list of vertices, where the vertices with no incoming edges |
| * come first |
| */ |
| public static <T> List<T> sort(Collection<T> vertices, EdgeRelation<? super T> edgeRelation) { |
| List<T> result = new ArrayList<T>(vertices.size()); |
| Set<T> visited = new HashSet<T>(); |
| for (T vertex : vertices) { |
| visit(vertices, edgeRelation, result, visited, vertex); |
| } |
| return result; |
| } |
| } |