package aima.core.environment.eightpuzzle;
import aima.core.search.framework.HeuristicFunction;
import aima.core.util.datastructure.XYLocation;
/**
* @author Ravi Mohan
*
*/
public class MisplacedTilleHeuristicFunction implements HeuristicFunction {
public double h(Object state) {
EightPuzzleBoard board = (EightPuzzleBoard) state;
return getNumberOfMisplacedTiles(board);
}
private int getNumberOfMisplacedTiles(EightPuzzleBoard board) {
int numberOfMisplacedTiles = 0;
if (!(board.getLocationOf(0).equals(new XYLocation(0, 0)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(1).equals(new XYLocation(0, 1)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(2).equals(new XYLocation(0, 2)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(3).equals(new XYLocation(1, 0)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(4).equals(new XYLocation(1, 1)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(5).equals(new XYLocation(1, 2)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(6).equals(new XYLocation(2, 0)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(7).equals(new XYLocation(2, 1)))) {
numberOfMisplacedTiles++;
}
if (!(board.getLocationOf(8).equals(new XYLocation(2, 2)))) {
numberOfMisplacedTiles++;
}
// Subtract the gap position from the # of misplaced tiles
// as its not actually a tile (see issue 73).
if (numberOfMisplacedTiles > 0) {
numberOfMisplacedTiles--;
}
return numberOfMisplacedTiles;
}
}