/// <summary>
/// Find the places that will force the other player to defend, put his
/// piece in a place that is not going to create a fork.
/// </summary>
/// <param name="playerPiece">
/// Flag for representing the diferent players.
/// </param>
/// <param name="result">
/// The result set for storing the values.
/// </param>
/// <param name="board">
/// The board to use.
/// </param>
/// <returns>
/// True if at least 1 possible wins was found.
/// </returns>
public static bool GetBlockForkingMove(bool playerPiece, BrainResult result, Board board)
{
// can the other player create a fork?
var outerResult = new BrainResult();
var fork = GetForkingMove(!playerPiece, outerResult, board, true);
if (fork && outerResult.Moves.Count > 0)
{
var tempBoard = board.Clone();
for (int i = 0; i < board.BoardSize; i++)
{
if (tempBoard.BoardArray[i] == 0)
{
tempBoard.BoardArray[i] = playerPiece ? 1 : -1;
var innerResult = new BrainResult();
if (GetWinningMove(playerPiece, 1, innerResult, tempBoard) // am I going to make two in a row
&& !outerResult.ContainsMove(tempBoard, i)) // this pos won't allow the user to fork
{
result.Moves.Add(board.GetMove(i));
return true;
}
tempBoard.BoardArray[i] = 0;
}
}
}
return false;
}
private void ComputerPlay()
{
var result = new BrainResult();
if (this.game.GetNewMove(result))
{
var move = result.Moves.First();
this.game.MakeMove(move.X, move.Y, false);
}
this.UpdateUI();
}
public bool GetNewMove(BrainResult result)
{
return GameBrain.GetWinningMove(false, 1, result, this.Board) // <-------- 1. Can we win?
|| GameBrain.GetWinningMove(true, 1, result, this.Board) // <------ 2. Can we stop you from winning?
|| GameBrain.GetForkingMove(false, result, this.Board) // <-------- 3. Can we create a fork?
|| GameBrain.GetBlockForkingMove(true, result, this.Board) // <---- 4. (a) Can we force you not to make a fork?
|| GameBrain.GetForkingMove(true, result, this.Board) // <--------- (b) Can we stop your fork?
|| GameBrain.GetCentreMove(result, this.Board) // <---------------- 5. Play in the centre
|| GameBrain.GetOppositeCornerMove(false, result, this.Board) // <- 6. Play the opposite corner if the opponent is in the corner.
|| GameBrain.GetEmptyCornerMove(result, this.Board) // <----------- 7. Play in a corner square.
|| GameBrain.GetEmptySideMove(result, this.Board); // <------------ 8. Play in a middle square on any of the 4 sides.
}
public static bool CheckForWin(bool vert, bool playerPiece, BrainResult result, Board board)
{
int outMax = vert ? board.BoardWidth : board.BoardSize;
int outStp = vert ? 1 : board.BoardWidth;
int inMax = vert ? board.BoardSize : board.BoardWidth;
int inStp = vert ? board.BoardWidth : 1;
int size = vert ? board.BoardHeight : board.BoardWidth;
BrainResult tempResult = new BrainResult();
for (int i = 0; i < outMax; i += outStp)
{
for (int j = 0; j < inMax; j += inStp)
{
if (board.IsSamePlayerPiece(playerPiece, i + j))
{
int x = vert ? j / board.BoardWidth : j;
int y = vert ? i : i / board.BoardWidth;
var move = vert ? new Move(y, x) : new Move(x, y);
tempResult.Moves.Add(move);
}
}
if (tempResult.Moves.Count == size)
{
break;
}
}
if (tempResult.Moves.Count == size)
{
foreach (var move in tempResult.Moves)
{
result.Moves.Add(move);
}
return true;
}
return false;
}
public static bool GetOppositeCornerMove(bool playerPiece, BrainResult result, Board board)
{
var corners = board.Corners.ToArray();
for (int i = 0; i < corners.Count(); i++)
{
if (board.IsSamePlayerPiece(!playerPiece, corners[i]))
{
var o = (i % 2 == 0) ? (1) : (-1); // either the one forward or backwards
var opp = corners[i + o];
if (board.BoardArray[board.GetIndex(opp.X, opp.Y)] == 0)
{
result.Moves.Add(opp);
return true;
}
}
}
return false;
}
public bool CheckForWin(BrainResult result)
{
return GameBrain.CheckForWin(false, result, this.Board)
|| GameBrain.CheckForWin(true, result, this.Board);
}
public static bool CheckForWin(bool playerPiece, BrainResult result, Board board)
{
return CheckForWin(true, playerPiece, result, board) // down
|| CheckForWin(false, playerPiece, result, board); // accross
}
/// <summary>
/// Play the center.
/// </summary>
/// <remarks>
/// If it is the first move of the game, playing on a corner gives the
/// other player more opportunities to make a mistake and may therefore
/// be the better choice.
/// However, it makes no difference between perfect players.
/// </remarks>
public static bool GetCentreMove(BrainResult result, Board board)
{
// only if the board has odd dimensions
if (board.BoardWidth % 2 != 0 && board.BoardHeight % 2 != 0)
{
var x = board.BoardWidth / 2;
var y = board.BoardHeight / 2;
var i = board.GetIndex(x, y);
// and if the place is empty
if (board.BoardArray[i] == 0)
{
result.Moves.Add(board.GetMove(i));
return true;
}
}
return false;
}
/// <summary>
/// If a player has two in a row, play the third to get three in a row.
/// </summary>
public static bool GetWinningMove(bool playerPiece, int minResults, BrainResult result, Board board)
{
return (GetStraightWinningMove(playerPiece, minResults, result, board) // staight win
|| GetDiagonalWinningMove(playerPiece, result, board)) // diagonal win
&& result.Moves.Count >= minResults; // are moves
}
/// <summary>
/// Find a place where, if the current player place his piece there,
/// will result in a win for that player.
/// </summary>
/// <param name="vert">
/// True if we are searching vertically, otherwise False if we are
/// searching horizontaly.
/// </param>
/// <param name="playerPiece">
/// Flag for representing the diferent players.
/// </param>
/// <param name="minResults">
/// The number of wins that need to be found before returning.
/// </param>
/// <param name="result">
/// The result set for storing the values.
/// </param>
/// <param name="board">
/// The board to use.
/// </param>
/// <returns>
/// True if at least <paramref name="minResults"/> possible wins were
/// found.
/// </returns>
public static bool GetStraightWinningMove(bool vert, bool playerPiece, int minResults, BrainResult result, Board board)
{
int outMax = vert ? board.BoardWidth : board.BoardSize;
int outStp = vert ? 1 : board.BoardWidth;
int inMax = vert ? board.BoardSize : board.BoardWidth;
int inStp = vert ? board.BoardWidth : 1;
int notPlayerPieceCount = 0;
for (int i = 0; i < outMax; i += outStp)
{
int x = 0;
for (int j = 0; j < inMax; j += inStp)
{
if (!board.IsSamePlayerPiece(playerPiece, i + j))
{
notPlayerPieceCount++;
if (notPlayerPieceCount > 1)
{
notPlayerPieceCount = 0;
break;
}
x = vert ? j / board.BoardWidth : j;
}
}
int y = vert ? i : i / board.BoardWidth;
var move = vert ? new Move(y, x) : new Move(x, y);
if (notPlayerPieceCount == 1 && board.IsValidMove(move.X, move.Y))
{
result.Moves.Add(move);
if (result.Moves.Count >= minResults)
{
return true;
}
}
}
return false;
}
public static bool GetStraightWinningMove(bool playerPiece, int minResults, BrainResult result, Board board)
{
return GetStraightWinningMove(true, playerPiece, minResults, result, board) // down
|| GetStraightWinningMove(false, playerPiece, minResults, result, board); // accross
}
/// <summary>
/// Using the given board, see if the other play can make any forks.
/// </summary>
/// <param name="playerPiece">
/// Flag for representing the diferent players.
/// </param>
/// <param name="board">
/// The board to use.
/// </param>
/// <returns>
/// True if at least 1 possible wins was found.
/// </returns>
public static bool GetOppositionForkingMove(bool playerPiece, Board board)
{
var tempBoard = board.Clone();
for (int i = 0; i < board.BoardSize; i++)
{
if (tempBoard.BoardArray[i] == 0)
{
tempBoard.BoardArray[i] = playerPiece ? 1 : -1;
var result = new BrainResult();
if (GetWinningMove(!playerPiece, 2, result, tempBoard))
{
return true;
}
tempBoard.BoardArray[i] = 0;
}
}
return false;
}
private void UpdateUI()
{
for (int i = 0; i < game.Board.BoardSize; i++)
{
var piece = game.Board.BoardArray[i];
if (piece == 0) buttons[i].Text = string.Empty;
else if (piece > 0) buttons[i].Text = "X";
else buttons[i].Text = "O";
}
BrainResult result = new BrainResult();
if (game.CheckForWin(result))
{
this.Text = string.Join(" : ", result.Moves.Select(x => x.ToString()));
}
}
/// <summary>
/// Fork by creating an opportunity where you can win in two ways.
/// </summary>
/// <param name="playerPiece">
/// Flag for representing the diferent players.
/// </param>
/// <param name="result">
/// The result set for storing the values.
/// </param>
/// <param name="board">
/// The board to use.
/// </param>
/// <param name="getAllForks">
/// Are we to get all the forks or stop after the first one is found.
/// </param>
/// <returns>
/// True if at least 1 possible forking move was found.
/// </returns>
public static bool GetForkingMove(bool playerPiece, BrainResult result, Board board, bool getAllForks = false)
{
var tempBoard = board.Clone();
for (int i = 0; i < board.BoardSize; i++)
{
if (tempBoard.BoardArray[i] == 0)
{
var piece = playerPiece ? 1 : -1;
tempBoard.BoardArray[i] = piece;
var outerResult = new BrainResult();
if (GetWinningMove(playerPiece, 2, outerResult, tempBoard))
{
var m = board.GetMove(i);
var innerResult = new BrainResult();
var notWin = !GetWinningMove(!playerPiece, 1, innerResult, tempBoard);
// switch last to the other player
var index = board.GetIndex(m.X, m.Y);
tempBoard.BoardArray[index] = piece * -1;
var notFork = !GetOppositionForkingMove(playerPiece, tempBoard);
if (notWin && notFork)
{
result.Moves.Add(m);
if (!getAllForks)
{
return true;
}
}
// switch back
tempBoard.BoardArray[index] = piece;
}
tempBoard.BoardArray[i] = 0;
}
}
return getAllForks && result.Moves.Count > 0;
}
public static bool GetEmptySideMove(BrainResult result, Board board)
{
for (int i = 0; i < board.BoardSize;i++)
{
// is empty and is not corner
if (board.BoardArray[i] == 0 && board.Corners.All(c => board.GetIndex(c) != i))
{
result.Moves.Add(board.GetMove(i));
return true;
}
}
return false;
}
public static bool GetEmptyCornerMove(BrainResult result, Board board)
{
var move = board.Corners.FirstOrDefault(m => board.BoardArray[board.GetIndex(m)] == 0);
if (move != null)
{
result.Moves.Add(move);
}
return move != null;
}
public static bool GetDiagonalWinningMove(bool reverse, bool playerPiece, BrainResult result, Board board)
{
// setup
int notPlayerPieceCount = 0;
// get direction values
int num = reverse ? board.BoardWidth - 1 : 0;
int step = reverse ? -1 : 1;
int x = 0, y = 0;
// find lines
for (int i = num; i < board.BoardSize - num; i += board.BoardWidth + step)
{
if (!board.IsSamePlayerPiece(playerPiece, i))
{
notPlayerPieceCount++;
if (notPlayerPieceCount > 1)
{
notPlayerPieceCount = 0;
break;
}
// get the xy co-ords
x = reverse ? i % board.BoardWidth : i / board.BoardWidth;
y = i / board.BoardHeight;
}
}
var move = new Move(x, y);
if (notPlayerPieceCount == 1 && board.IsValidMove(x, y))
{
// we found a place
result.Moves.Add(move);
return true;
}
// no place
return false;
}
public static bool GetDiagonalWinningMove(bool playerPiece, BrainResult result, Board board)
{
return GetDiagonalWinningMove(false, playerPiece, result, board) // top left to bottom right
|| GetDiagonalWinningMove(true, playerPiece, result, board); // top right to bottom left
}
