/**
* 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.mahout.ga.watchmaker.travellingsalesman;
import java.util.List;
import org.uncommons.watchmaker.framework.FitnessEvaluator;
/**
* Fitness evalator that measures the total distance of a route in the travelling salesman problem. The
* fitness score of a route is the total distance (in km). A route is represented as a list of cities in the
* order that they will be visited. The last leg of the journey is from the last city in the list back to the
* first.
*
* <br>
* The original code is from <b>the Watchmaker project</b> (https://watchmaker.dev.java.net/).
*/
public class RouteEvaluator implements FitnessEvaluator<List<String>> {
private final DistanceLookup distances;
/**
* @param distances
* Provides distances between a set of cities.
*/
public RouteEvaluator(DistanceLookup distances) {
this.distances = distances;
}
/**
* Calculates the length of an evolved route.
*
* @param candidate
* The route to evaluate.
* @param population
* {@inheritDoc}
* @return The total distance (in kilometres) of a journey that visits each city in order and returns to the
* starting point.
*/
@Override
public double getFitness(List<String> candidate, List<? extends List<String>> population) {
int totalDistance = 0;
int cityCount = candidate.size();
for (int i = 0; i < cityCount; i++) {
int nextIndex = i < cityCount - 1 ? i + 1 : 0;
totalDistance += distances.getDistance(candidate.get(i), candidate.get(nextIndex));
}
return totalDistance;
}
/**
* {@inheritDoc} Returns false since shorter distances represent fitter candidates.
*
* @return false
*/
@Override
public boolean isNatural() {
return false;
}
}