public bool isGoalState(Object state)
{
NQueensBoard board = (NQueensBoard)state;
return(board.getNumberOfQueensOnBoard() == board.getSize() &&
board.getNumberOfAttackingPairs() == 0);
}
public Object result(Object s, Action a)
{
if (a is QueenAction)
{
QueenAction qa = (QueenAction)a;
NQueensBoard board = (NQueensBoard)s;
NQueensBoard newBoard = new NQueensBoard(board.getSize());
newBoard.setBoard(board.getQueenPositions());
if (qa.getName() == QueenAction.PLACE_QUEEN)
{
newBoard.AddQueenAt(qa.getLocation());
}
else if (qa.getName() == QueenAction.REMOVE_QUEEN)
{
newBoard.removeQueenFrom(qa.getLocation());
}
else if (qa.getName() == QueenAction.MOVE_QUEEN)
{
newBoard.moveQueenTo(qa.getLocation());
}
s = newBoard;
}
// if action is not understood or is a NoOp
// the result will be the current state.
return(s);
}
public HashSet <Action> actions(Object state)
{
HashSet <Action> actions = new LinkedHashSet <Action>();
NQueensBoard board = (NQueensBoard)state;
for (int i = 0; i < board.getSize(); i++)
{
for (int j = 0; j < board.getSize(); j++)
{
XYLocation loc = new XYLocation(i, j);
if (!board.queenExistsAt(loc))
{
actions
.Add(new QueenAction(QueenAction.MOVE_QUEEN,
loc));
}
}
}
return(actions);
}
//
// START - Interface FitnessFunction
public double getValue(String individual)
{
double fitness = 0;
NQueensBoard board = getBoardForIndividual(individual);
int boardSize = board.getSize();
// Calculate the number of non-attacking pairs of queens (refer to AIMA
// page 117).
List <XYLocation> qPositions = board.getQueenPositions();
for (int fromX = 0; fromX < (boardSize - 1); fromX++)
{
for (int toX = fromX + 1; toX < boardSize; toX++)
{
int fromY = qPositions.get(fromX).getYCoOrdinate();
bool nonAttackingPair = true;
// Check right beside
int toY = fromY;
if (board.queenExistsAt(new XYLocation(toX, toY)))
{
nonAttackingPair = false;
}
// Check right and above
toY = fromY - (toX - fromX);
if (toY >= 0)
{
if (board.queenExistsAt(new XYLocation(toX, toY)))
{
nonAttackingPair = false;
}
}
// Check right and below
toY = fromY + (toX - fromX);
if (toY < boardSize)
{
if (board.queenExistsAt(new XYLocation(toX, toY)))
{
nonAttackingPair = false;
}
}
if (nonAttackingPair)
{
fitness += 1.0;
}
}
}
return(fitness);
}
public HashSet <Action> actions(Object state)
{
NQueensBoard board = (NQueensBoard)state;
HashSet <Action> actions = new LinkedHashSet <Action>();
int numQueens = board.getNumberOfQueensOnBoard();
int boardSize = board.getSize();
for (int i = 0; i < boardSize; i++)
{
XYLocation newLocation = new XYLocation(numQueens, i);
if (!(board.isSquareUnderAttack(newLocation)))
{
actions.Add(new QueenAction(QueenAction.PLACE_QUEEN,
newLocation));
}
}
return(actions);
}