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//=============================================================================
// Copyright 2006-2010 Daniel W. Dyer
//
// 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.uncommons.watchmaker.examples.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.
* @author Daniel Dyer
*/
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.
*/
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
*/
public boolean isNatural()
{
return false;
}
}
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