package aima.core.environment.eightpuzzle;
import aima.core.search.framework.HeuristicFunction;
import aima.core.util.datastructure.XYLocation;
/**
* @author Ravi Mohan
*
*/
public class ManhattanHeuristicFunction implements HeuristicFunction {
public double h(Object state) {
EightPuzzleBoard board = (EightPuzzleBoard) state;
int retVal = 0;
for (int i = 1; i < 9; i++) {
XYLocation loc = board.getLocationOf(i);
retVal += evaluateManhattanDistanceOf(i, loc);
}
return retVal;
}
public int evaluateManhattanDistanceOf(int i, XYLocation loc) {
int retVal = -1;
int xpos = loc.getXCoOrdinate();
int ypos = loc.getYCoOrdinate();
switch (i) {
case 1:
retVal = Math.abs(xpos - 0) + Math.abs(ypos - 1);
break;
case 2:
retVal = Math.abs(xpos - 0) + Math.abs(ypos - 2);
break;
case 3:
retVal = Math.abs(xpos - 1) + Math.abs(ypos - 0);
break;
case 4:
retVal = Math.abs(xpos - 1) + Math.abs(ypos - 1);
break;
case 5:
retVal = Math.abs(xpos - 1) + Math.abs(ypos - 2);
break;
case 6:
retVal = Math.abs(xpos - 2) + Math.abs(ypos - 0);
break;
case 7:
retVal = Math.abs(xpos - 2) + Math.abs(ypos - 1);
break;
case 8:
retVal = Math.abs(xpos - 2) + Math.abs(ypos - 2);
break;
}
return retVal;
}
}