/*****************************************************************
* 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.
****************************************************************/
/* ====================================================================
*
* Copyright(c) 2003, Andriy Shapochka
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* 2. Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* 3. Neither the name of the ASHWOOD nor the
* names of its contributors may be used to endorse or
* promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ====================================================================
*
* This software consists of voluntary contributions made by
* individuals on behalf of the ASHWOOD Project and was originally
* created by Andriy Shapochka.
*
*/
package org.apache.cayenne.ashwood.graph;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
/**
* @since 3.1
*/
public class IndegreeTopologicalSort<E> implements Iterator<E> {
private Digraph<E, ?> digraph;
private List<E> vertices = new LinkedList<>();
private Map<E, InDegree> inDegrees = new HashMap<>();
private ListIterator<E> current;
public IndegreeTopologicalSort(Digraph<E, ?> digraph) {
this.digraph = digraph;
for (Iterator<E> i = digraph.vertexIterator(); i.hasNext();) {
E vertex = i.next();
vertices.add(vertex);
inDegrees.put(vertex, new InDegree(digraph.incomingSize(vertex)));
}
current = vertices.listIterator();
}
public boolean hasNext() {
return !vertices.isEmpty();
}
public E next() {
boolean progress = true;
while (hasNext()) {
if (!current.hasNext()) {
if (!progress)
break;
progress = false;
current = vertices.listIterator();
}
E vertex = current.next();
InDegree indegree = inDegrees.get(vertex);
if (indegree.value == 0) {
removeVertex(vertex);
current.remove();
return vertex;
}
}
return null;
}
private void removeVertex(E vertex) {
for (ArcIterator<E, ?> i = digraph.outgoingIterator(vertex); i.hasNext();) {
i.next();
E dst = i.getDestination();
InDegree indegree = inDegrees.get(dst);
indegree.value--;
}
}
public void remove() {
throw new UnsupportedOperationException("Method remove() not supported.");
}
private static class InDegree {
int value;
InDegree(int value) {
InDegree.this.value = value;
}
}
}