org.bbottema.javareflection.util.graph.NodePathComparator Maven / Gradle / Ivy

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Java Reflection provides a small package with nifty reflection features that will help with finding constructors, methods and value conversions

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/*
 * Copyright (C) ${project.inceptionYear} Benny Bottema ([email protected])
 *
 * Licensed 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.bbottema.javareflection.util.graph;

import java.util.Comparator;
import java.util.List;

import static org.bbottema.javareflection.util.MiscUtil.trustedCast;

class NodePathComparator implements Comparator>> {
	
	private static final NodePathComparator INSTANCE = new NodePathComparator<>();
	
	static  NodePathComparator INSTANCE() {
		return trustedCast(INSTANCE);
	}
	
	private NodePathComparator() {
	}
	
	@Override
	public int compare(List> nodes1, List> nodes2) {
		return sumNodes(nodes1).compareTo(sumNodes(nodes2));
	}
	
	/**
	 * Since given list of nodes represents a connected path, each subsequent nodes will exist in each previous node' toNodes collection.
	 * 
	 * We need to calculate the distance this way, since Dijkstra's algorithm mutates the distance property for a single shortes path to a
	 * starting node.
	 */
	private Integer sumNodes(List> nodes) {
		Node currentFromNode = null;
		int nodesCost = 0;
		for (Node nodeInPath : nodes) {
			if (currentFromNode != null) {
				nodesCost += currentFromNode.getToNodes().get(nodeInPath);
			}
			currentFromNode = nodeInPath;
		}
		return nodesCost;
	}
}