public override void Move(Board b)
{
{
//Create a new game state for the root of the state space
GameState gameState = new GameState(GameState.State.initial, b, this, null, cell, true);
//Set the state as the root
MiniMaxTree m = new MiniMaxTree(gameState);
//Find children states if they exist
m.GenerateStates(gameState, 4, true);
//The value returned by the recursive minimax function
int value = m.MiniMax(gameState, 4, true);
cell = null;
foreach(GameState child in gameState.GetChildren())
{
if (child.GetHeuristicValue() == value)
{
cell = child.GetCell();
}
}
//Set the cell on the playing board
b.getCell(cell.getRow(), cell.getColumn()).setState((int)cell.getState());
//if a row exists above this cell, make it playable
if (cell.getRow() != 0)
{
b.getCell(cell.getRow() - 1, cell.getColumn()).isPlayable(true);
}
//Test if the game is over
if(MiniMaxTree.TerminalTest(cell))
{
b.printBoard();
Console.WriteLine("GameOver: " + this.getColorToString() + " wins");
b.isGameOver(true);
}
moveCount++;
}
}
public GameState(State s, Board b, Player p, GameState parent, Cell c, Boolean mp)
{
maxPlayer = mp;
state = s;
cell = c;
board = b;
player = p;
this.parent = parent;
children = new List<GameState>();
Region.findConnectedCells(b);
b.UpdateCellObservers();
if(MiniMaxTree.TerminalTest(cell) && state != GameState.State.initial)
{
state = GameState.State.terminal;
if (maxPlayer)
{
heuristicValue = MiniMaxTree.MIN_VALUE;
}
else
heuristicValue = MiniMaxTree.MAX_VALUE;
}
}
public int FindHeuristicValue(GameState gs)
{
int value = 0;
//The count of connectCells a cell contains
int bestCount = 0;
int connectR = Board.GetConnectR();
if(gs.GetState().Equals(GameState.State.terminal))
{
return gs.GetHeuristicValue();
}
//if true it is maxPlayers turn and the board needs to be evaluate to minimize min's score
if(gs.isMaxPlayer())
{
//check if max can make a killer move
foreach(Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer()))
{
if(cell.isTerminal() > 0)
{
value = MAX_VALUE;
return value;
}
}
//check if it is impossible to prevent min from winning
if(gs.GetCell().isTerminal() > 1)
{
value = MIN_VALUE;
return value;
}
//check if min can make a killer move
foreach (Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer().getOpponent()))
{
if (cell.isTerminal() == 1)
{
value = MIN_VALUE / 2;
return value;
}
}
//last resort - find the move that gives the most possibilites for connect 4
foreach(Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer()))
{
int count = 0;
foreach(KeyValuePair<int, HashSet<Cell>> c in cell.GetObservers())
{
count = count + c.Value.Count;
}
foreach(KeyValuePair<int, List<Cell>> k in cell.GetConnectedCells())
{
count = count + k.Value.Count;
}
if(count > bestCount)
{
bestCount = count;
}
}
value = bestCount;
return value;
}
//It is not max's turn
else
{
//check if min can make a killer move
foreach (Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer().getOpponent()))
{
if (cell.isTerminal() > 0)
{
value = MIN_VALUE;
return value;
}
}
//check if it is impossible to prevent max from winning
if (gs.GetCell().isTerminal() > 1)
{
value = MAX_VALUE;
return value;
}
//check if max can make a killer move
foreach (Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer()))
{
if (cell.isTerminal() == 1)
{
value = MAX_VALUE / 2;
return value;
}
}
}
//last resort - find the move that gives the most possibilites for connect 4
foreach (Cell cell in gs.GetBoard().getPlayerCells(gs.GetPlayer().getOpponent()))
{
int count = 0;
foreach (KeyValuePair<int, HashSet<Cell>> c in cell.GetObservers())
{
count = count + c.Value.Count;
}
foreach (KeyValuePair<int, List<Cell>> k in cell.GetConnectedCells())
{
count = count + k.Value.Count;
}
if (count > bestCount)
{
bestCount = count;
}
}
value = bestCount;
return value;
}
public MiniMaxTree(GameState gs)
{
root = gs;
}
public int MiniMax(GameState gs, int depth, Boolean maxPlayer)
{
//base case
if (depth == 0 || gs.GetState().Equals(GameState.State.terminal))
{
return FindHeuristicValue(gs);
}
if(maxPlayer)
{
int bestValue = MIN_VALUE;
foreach(GameState child in gs.GetChildren())
{
int value = MiniMax(child, depth - 1, false);
if (value.CompareTo(bestValue) > 0)
{
gs.SetHeuristicValue(value);
bestValue = value;
}
}
return bestValue;
}
else
{
int bestValue = MAX_VALUE;
foreach (GameState child in gs.GetChildren())
{
int value = MiniMax(child, depth - 1, true);
if(value.CompareTo(bestValue) < 0)
{
gs.SetHeuristicValue(value);
bestValue = value;
}
}
return bestValue;
}
}
public void GenerateStates(GameState gs, int depth, Boolean maxPlayer)
{
if(depth == 0 || gs.GetState().Equals(GameState.State.terminal))
{
return;
}
gs.FindChildrenStates(maxPlayer);
foreach(GameState child in gs.GetChildren())
{
if (maxPlayer)
{
GenerateStates(child, depth - 1, false);
}
else
GenerateStates(child, depth - 1, true);
}
}
// private methods
private void gameOverCheck(int row, int column, out GameState gameState)
{
gameState = GameState.notWon;
// check horizontal for a win
checkHorizontal(row, column, out gameState);
// check vertical for a win
if (gameState == GameState.notWon)
{
checkVertical(row, column, out gameState);
} // end if
// check diagonal (up and right, down and left) for a win
if (gameState == GameState.notWon)
{
checkDiagonal(row, column, out gameState);
} // end if
// check antidiagonal (up and left, down and right) for a win
if (gameState == GameState.notWon)
{
checkAntiDiagonal(row, column, out gameState);
} // end if
// check to see if it is a draw
if (gameState == GameState.notWon && numberOfMoves >= 42)
{
gameState = GameState.draw;
} // end if
}
private void checkVertical(int row, int column, out GameState gameState)
{
gameState = GameState.notWon;
int numberInARow = 1;
bool noBreaks = true;
// compare to the next one up
int nextRow = row + 1; // row is y
int nextColumn = column; // column is x
while ((nextRow < gameBoard.GetLength(ROW)) && (numberInARow < 4) && (noBreaks)) // check up
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextRow++; // look at the next space up
} // end while
// reset the row to compare to the next one down
nextRow = row - 1; // row is y
noBreaks = true; // reset so we can look the other direction
while ((nextRow >= 0) && (numberInARow < 4) && (noBreaks)) // check down
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextRow--; // look at the next space down
} // end while
if (numberInARow >= 4)
{
gameState = GameState.won;
} // end if
}
private void checkHorizontal(int row, int column, out GameState gameState)
{
gameState = GameState.notWon;
int numberInARow = 1;
bool noBreaks = true;
// compare to the next one on the right
int nextRow = row; // row is y
int nextColumn = column + 1; // column is x
while ((nextColumn < gameBoard.GetLength(COLUMN)) && (numberInARow < 4) && (noBreaks)) // check to the right
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextColumn++; // look at the next space to the right
} // end while
// reset the column to compare to the next one on the left
nextColumn = column - 1; // column is x
noBreaks = true; // reset so we can look the other direction
while ((nextColumn >= 0) && (numberInARow < 4) && (noBreaks)) // check to the left
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextColumn--; // look at the next space to the left
} // end while
if (numberInARow >= 4)
{
gameState = GameState.won;
} // end if
}
private void checkDiagonal(int row, int column, out GameState gameState)
{
gameState = GameState.notWon;
int numberInARow = 1;
bool noBreaks = true;
// row is y, column is x
if (((row - column) < 3) && ((row + (6 - column)) > 2)) // make sure we are not comparing if it is in the top left or bottom right corner
{
// compare to the next one up and right
int nextRow = row + 1; // row is y
int nextColumn = column + 1; // column is x
while (((nextRow < gameBoard.GetLength(ROW)) && (nextColumn < gameBoard.GetLength(COLUMN))) && (numberInARow < 4) && (noBreaks)) // check up and right
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextRow++; // look at the next space up
nextColumn++; // look at the next space to the right
} // end while
// reset the row to compare to the next one down and left
nextRow = row - 1; // row is y
nextColumn = column - 1;
noBreaks = true; // reset so we can look the other direction
while (((nextRow >= 0) && (nextColumn >= 0)) && (numberInARow < 4) && (noBreaks)) // check down and left
{
compareColors(row, column, nextRow, nextColumn, ref numberInARow, ref noBreaks);
nextRow--; // look at the next space down
nextColumn--; // look at the next space to the left
} // end while
if (numberInARow >= 4)
{
gameState = GameState.won;
} // end if
} // end if
}
public void FindChildrenStates(Boolean maxPlayer)
{
GameState gs;
for(int i = 0; i < board.GetWidth(); i++)
{
for(int j = 0; j < board.GetLength(); j++)
{
if(board.getCell(j,i).getState().Equals(Cell.CellState.empty))
{
if (board.getCell(j, i).isPlayable())
{
Board b = new Board(board);
Cell cell = b.getCell(j, i);
if (maxPlayer)
{
cell.setState(player.getColor());
}
else
{
cell.setState(player.getOpponent().getColor());
}
if (j != 0)
{
b.getCell(j - 1, i).isPlayable(true);
}
gs = new GameState(GameState.State.transition, b, player, this, cell, !maxPlayer);
children.Add(gs);
}
}
else
break;
}
}
}
public void SetState(GameState.State s)
{
state = s;
}
