/// <summary>
/// Max value search function
/// </summary>
/// <param name="state">The current state of the game</param>
/// <param name="alpha">highest alpha found</param>
/// <param name="beta">lowest beta found</param>
/// <param name="depth">depth current state is at</param>
/// <returns>The best max value</returns>
public int MaxValue(CheckersGameState state, int alpha, int beta, int depth)
{
//increase depth
depth++;
maxDepth = (depth > maxDepth) ? depth : maxDepth;
//Evaluate the state
int utilityValue = Evaluate(state);
//If the state is terminal or if the cuttoff is reached, return the value
if (utilityValue == MAX_INT || utilityValue == MIN_INT ||
depth == cutoff + iterativeDepth || (DateTime.Now - startTime).TotalSeconds > 55)
{
return(utilityValue);
}
//integer value used to determine alpha
int value = MIN_INT;
//A temporary gamestate to prevent anything in the actual game from changing
CheckersGameState tempState;
//The loop below finds every possible action from this state,
//then using the temporary state, it will do the action,
//and pass that state into the minValue function to find the largest possible value for alpha
foreach (CheckersPiece piece in state.moveablePieces)
{
state.doGamePieceAction(piece);
foreach (GameMove action in state.activeGamePiece.getPossibleMoves())
{
tempState = new CheckersGameState(state);
nodes++;
if (tempState.doTileAction(tempState.gameBoard.getTileAt(action.destinationPosition)) == true)
{
tempState.activeGamePiece.Update(tempState);
}
value = Math.Max(value, MinValue(tempState, alpha, beta, depth));
//if alpha becomes greater than or equal to beta prune the tree
if (value >= beta)
{
maxPruned++;
return(value);
}
if (alpha < value)
{
alpha = value;
//if we are in the actual state of the game, that means we found a new best move
if (depth == 1)
{
bestMove = action;
}
}
}
}
return(value);
}
/// <summary>
/// Copy constructor for a game move.
/// This constructor is used for creating temporary game states.
/// </summary>
/// <param name="move">The move to copy</param>
public GameMove(GameMove move)
{
movePiece = move.movePiece;
capturedPieces = new List <CheckersPiece>();
foreach (CheckersPiece piece in move.capturedPieces)
{
capturedPieces.Add(new CheckersPiece(piece));
}
destinationPosition = new Vector2(move.destinationPosition.X, move.destinationPosition.Y);
originalPosition = new Vector2(move.originalPosition.X, move.originalPosition.Y);
}
/// <summary>
/// Function that is called whenever it is the turn of the AI to do its move
/// </summary>
public void doAiMove()
{
if (didAiMove == false)
{
bool onlyOneMove = false;
//Check if theres only 1 moveable piece
if (currentState.moveablePieces.Count == 1)
{
//If there only 1 moveable piece and only 1 available action, set best move to that move
if (currentState.moveablePieces.First().getPossibleMoves().Count == 1)
{
bestMove = currentState.moveablePieces.First().getPossibleMoves().First();
onlyOneMove = true;
Console.WriteLine("Only one move was available - Alpha-beta wasn't required"
+ "\n--------------------------------------------------------");
}
}
//If there is more than one move run algorithm
if (onlyOneMove == false)
{
int bestMoveValue = AlphaBetaSearch(new CheckersGameState(currentState));
//if the algorithm determines that the AI will win or lose regardless of which move,
//then make the ai do the first possible move it can
if (bestMoveValue == MIN_INT || bestMoveValue == MAX_INT)
{
bestMove = currentState.moveablePieces.First().getPossibleMoves()[0];
}
//if algorithm took 50 or more seconds to run, it has reach time cutoff
if ((endTime - startTime).TotalSeconds >= 55)
{
Console.Write("Tree reached time cutoff of 55 seconds"
+ "\n--Max Depth: " + maxDepth
+ "\n--Cut Off Depth: " + (cutoff + iterativeDepth));
//Reached time cutoff - reduce the cutoff by 1/4
float actualCutoff = 0.75f * (cutoff + iterativeDepth);
iterativeDepth = (((int)actualCutoff - cutoff) > 0) ? (int)actualCutoff - cutoff : 0;
}
//Else if maxDepth is equal to the cutoff depth, that means the tree reached cutoff level
else if (maxDepth == cutoff + iterativeDepth)
{
Console.Write("Tree reached cut off"
+ "\n--Cut Off Depth: " + (cutoff + iterativeDepth));
//Since alpha-beta was able to finish in reasonable time (< 50s)
// and the cutoff was reached, increased by 1 + (1/4)number of turns passed
iterativeDepth = 1 + (int)(currentState.numTurnsPassed * 0.25);
}
//else the tree completed before reaching cutoff
else
{
Console.Write("Tree completed before reaching cut off"
+ "\n--Max Depth: " + maxDepth
+ "\n--Cut Off Depth: " + (cutoff + iterativeDepth));
}
Console.WriteLine("\n--Nodes Generated: " + nodes
+ "\n--# times pruning occured in MAX-VALUE: " + maxPruned
+ "\n--# times pruning occured in MIN-VALUE: " + minPruned
+ "\nFound Move in: " + (endTime - startTime).TotalSeconds
+ "seconds\n--------------------------------------------------------");
//AI is completed sleep the thread
Thread.Sleep(1000);
}
//Do the actual move
CheckersPiece movePiece = bestMove.movePiece;
currentState.doGamePieceAction(currentState.getPiece(movePiece.getColor(), movePiece.position));
//Set now to when the delay for the AI to actually do the move to now
didAiMove = true;
aiMoveStart = DateTime.Now;
}
else
{
//If the delay for an AI to do the move has been reached do the move
if ((DateTime.Now - aiMoveStart).TotalSeconds > aiTimeDelay)
{
if (currentState.doTileAction(currentState.gameBoard.getTileAt(bestMove.destinationPosition)) == true)
{
currentState.activeGamePiece.Update(currentState);
didAiMove = false;
}
}
}
}
/// <summary>
/// Function that will recursively find all the jump sequences possible by this piece
/// </summary>
/// <param name="tilePosition">The position of the tile to check jumps from</param>
/// <param name="gameBoard">The gameboard</param>
/// <param name="gameState">The current gamestate</param>
/// <returns>A list of possible jumps</returns>
public List <GameMove> getJumps(Vector2 tilePosition, CheckersBoard gameBoard, CheckersGameState gameState)
{
List <GameMove> jumps = new List <GameMove>();
//Get all the possible tiles that could result with a jump
BoardTile topLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y - 1);
BoardTile topRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y - 1);
BoardTile bottomLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y + 1);
BoardTile bottomRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y + 1);
BoardTile topLeftJumpTile = gameBoard.getTileAt((int)tilePosition.X - 2, (int)tilePosition.Y - 2);
BoardTile topRightJumpTile = gameBoard.getTileAt((int)tilePosition.X + 2, (int)tilePosition.Y - 2);
BoardTile bottomLeftJumpTile = gameBoard.getTileAt((int)tilePosition.X - 2, (int)tilePosition.Y + 2);
BoardTile bottomRightJumpTile = gameBoard.getTileAt((int)tilePosition.X + 2, (int)tilePosition.Y + 2);
//Set the enemy color
PieceColor enemyColor;
if (this.color == PieceColor.Black)
{
enemyColor = PieceColor.White;
}
else
{
enemyColor = PieceColor.Black;
}
//The below four if-elses will basically determine if there was a piece of the enemy color was jumped over
//by moving to a tile 2 diagonal tiles away. If there was a jump, it will mark the piece that it just jumped over
//and then recursively look for any other following jumps from that tile.
if (topLeftTile != null && topLeftTile.getOccupiedStatus() == enemyColor)
{
//Get the piece that was jumped over
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, topLeftTile.position);
if (topLeftJumpTile != null && topLeftJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//mark the piece as jumped over
adjacentPiece.justJumpedOver = true;
//Find any jumps from the new tile position
List <GameMove> sequenceJumps = getJumps(topLeftJumpTile.position, gameBoard, gameState);
//If there was no following jump then add the jump to the list of jump
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, topLeftJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
//Else for each following jump, add the piece the first jump captured to the list of captured pieces
else
{
foreach (GameMove jump in sequenceJumps)
{
//GameMove newJump = (new GameMove(this, jump.destinationPosition));
//jump.capturedPieces = jump.capturedPieces;
jump.capturedPieces.Add(adjacentPiece);
jumps.Add(jump);
}
}
}
}
if (topRightTile != null && topRightTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, topRightTile.position);
if (topRightJumpTile != null && topRightJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(topRightJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, topRightJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
if (bottomLeftTile != null && bottomLeftTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, bottomLeftTile.position);
if (bottomLeftJumpTile != null && bottomLeftJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(bottomLeftJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, bottomLeftJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
if (bottomRightTile != null && bottomRightTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, bottomRightTile.position);
if (bottomRightJumpTile != null && bottomRightJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(bottomRightJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, bottomRightJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
return(jumps);
}
