public Minimax(GameEngine game, int depth)
{
this.game = game;
this.definedDepth = depth;
this.current = new State(game.currentState.Grid, GameEngine.PLAYER);
this.deck = new Deck();
}
public MCTS(GameEngine gameEngine)
{
this.gameEngine = gameEngine;
this.deck = new Deck();
this.currentState = new State(BoardHelper.CloneGrid(this.gameEngine.currentState.Grid), GameEngine.PLAYER);
this.random = new Random();
}
public GameEngine()
{
deck = new Deck();
int[][] grid = initializeGrid();
currentState = new State(grid, COMPUTER);
UpdatePeekCard();
}
public Node(Move move, Node parent, State state, Deck deck)
{
this.state = state;
this.generatingMove = move;
this.parent = parent;
this.results = 0;
this.visits = 0;
this.children = new List<Node>();
this.untriedMoves = state.GetMoves(deck);
}
// Returns all available moves in the state
internal List<Move> GetMoves(Deck deck)
{
if (player == GameEngine.PLAYER)
{
return GetAllPlayerMoves();
}
else
{
return GetAllComputerMoves(deck);
}
}
// Returns a list of all available computer moves given a deck
public List<Move> GetAllComputerMoves(Deck deck)
{
IEnumerable<int> cardsLeft = deck.GetAllCards().Distinct(); // get all distinct cards left
List<Move> moves = new List<Move>();
foreach (int card in cardsLeft)
{
switch (((PlayerMove)generatingMove).Direction)
{
case DIRECTION.LEFT:
return AddComputerMovesAfterLeft(moves, card);
case DIRECTION.RIGHT:
return AddComputerMovesAfterRight(moves, card);
case DIRECTION.UP:
return AddComputerMovesAfterUp(moves, card);
case DIRECTION.DOWN:
return AddComputerMovesAfterDown(moves, card);
default:
throw new Exception();
}
}
return moves;
}
// To take advantage of the fact that we can count cards
private void UpdateDeckMemory(int card, bool firstMove)
{
if (firstMove)
{
for (int i = 0; i < GameEngine.COLUMNS; i++)
{
for (int j = 0; j < GameEngine.ROWS; j++)
{
if (current.Grid[i][j] != 0)
{
deck.Remove(current.Grid[i][j]);
}
}
}
}
else
{
deck.Remove(card); // remove the observed card from our deck memory
if (deck.IsEmpty())
{
deck = new Deck();
}
}
}
// Recursive part of iterative deepening
private Tuple<Move, bool> RecursiveIterativeDeepening(State state, int depth, double alpha, double beta, int timeLimit, Stopwatch timer, Deck deck)
{
Move bestMove;
if (depth == 0 || state.IsGameOver())
{
if (state.Player == GameEngine.PLAYER)
{
bestMove = new PlayerMove(); // default constructor creates dummy action
bestMove.Score = AI.Evaluate(state);
return new Tuple<Move, Boolean>(bestMove, true);
}
else if (state.Player == GameEngine.COMPUTER)
{
bestMove = new ComputerMove(); // default constructor creates dummy action
bestMove.Score = AI.Evaluate(state);
return new Tuple<Move, Boolean>(bestMove, true);
}
else
{
throw new Exception();
}
}
if (state.Player == GameEngine.PLAYER){
bestMove = new PlayerMove();
double highestScore = Double.MinValue, currentScore = Double.MinValue;
List<Move> moves = state.GetAllMoves();
foreach (Move move in moves)
{
State resultingState = state.ApplyMove(move);
currentScore = RecursiveIterativeDeepening(resultingState, depth - 1, alpha, beta, timeLimit, timer, deck).Item1.Score;
if (currentScore > highestScore)
{
highestScore = currentScore;
bestMove = (PlayerMove)move;
}
alpha = Math.Max(alpha, highestScore);
if (beta <= alpha)
break;
if (timer.ElapsedMilliseconds > timeLimit)
{
bestMove.Score = highestScore;
return new Tuple<Move, Boolean>(bestMove, false); // recursion not completed, return false
}
}
bestMove.Score = highestScore;
return new Tuple<Move, Boolean>(bestMove, true);
}
else
{
bestMove = new ComputerMove();
double lowestScore = Double.MaxValue, currentScore = Double.MaxValue;
List<Move> moves = null;
if (depth == definedDepth - 1)
{
int nextCard = game.nextCard;
moves = state.GetAllComputerMoves(nextCard);
}
else
{
if (deck.IsEmpty()) deck = new Deck();
moves = state.GetAllComputerMoves(deck);
}
foreach (Move move in moves)
{
deck.Remove(((ComputerMove)move).Card);
State resultingState = state.ApplyMove(move);
currentScore = RecursiveIterativeDeepening(resultingState, depth - 1, alpha, beta, timeLimit, timer, deck).Item1.Score;
if (currentScore < lowestScore)
{
lowestScore = currentScore;
bestMove = (ComputerMove)move;
}
beta = Math.Min(beta, lowestScore);
if (beta <= alpha)
break;
deck.Add(((ComputerMove)move).Card);
if (timer.ElapsedMilliseconds > timeLimit)
{
bestMove.Score = lowestScore;
return new Tuple<Move, Boolean>(bestMove, false); // recursion not completed, return false
}
}
bestMove.Score = lowestScore;
return new Tuple<Move, Boolean>(bestMove, true);
}
}
// Runs an entire game using a parallelized version of iterative deepening minimax
private Move ParallelIterativeDeepening(State state, int timeLimit, Deck deck)
{
Move bestMove = new PlayerMove();
List<Move> moves = state.GetMoves(deck);
ConcurrentBag<Tuple<double, Move>> scores = new ConcurrentBag<Tuple<double, Move>>();
if (moves.Count == 0)
{
// game over
return bestMove;
}
// create the resulting states before starting the threads
List<State> resultingStates = new List<State>();
foreach (Move move in moves)
{
State resultingState = state.ApplyMove(move);
resultingStates.Add(resultingState);
}
Parallel.ForEach(resultingStates, resultingState =>
{
double score = IterativeDeepening(resultingState, timeLimit, deck.Clone()).Score;
scores.Add(new Tuple<double, Move>(score, resultingState.GeneratingMove));
});
// find the best score
double highestScore = Double.MinValue;
foreach (Tuple<double, Move> score in scores)
{
PlayerMove move = (PlayerMove)score.Item2;
if (score.Item1 > highestScore)
{
highestScore = score.Item1;
bestMove = score.Item2;
}
}
return bestMove;
}
// Starts the time limited Monte Carlo Tree Search and returns the best child node
// resulting from the search
public Node TimeLimitedMCTS(State rootState, int timeLimit, Deck deck)
{
Stopwatch timer = new Stopwatch();
Node bestNode = null;
while (bestNode == null && !rootState.IsGameOver())
{
timer.Start();
Node rootNode = TimeLimited(rootState, timeLimit, timer, deck);
bestNode = FindBestChild(rootNode.Children);
timeLimit += 10;
timer.Reset();
}
return bestNode;
}
// MIN part of Minimax
Move Min(State state, int depth, double alpha, double beta)
{
ComputerMove bestMove = new ComputerMove();
double lowestScore = Double.MaxValue, currentScore = Double.MaxValue;
List<Move> moves = null;
if (depth == definedDepth - 1)
{
int nextCard = game.nextCard;
moves = state.GetAllComputerMoves(nextCard);
}
else
{
if (deck.IsEmpty()) deck = new Deck();
moves = state.GetAllComputerMoves(deck);
}
foreach (Move move in moves)
{
deck.Remove(((ComputerMove)move).Card);
State resultingState = state.ApplyMove(move);
currentScore = MinimaxAlgorithm(resultingState, depth - 1, alpha, beta, deck).Score;
if (currentScore < lowestScore)
{
lowestScore = currentScore;
bestMove = (ComputerMove)move;
}
beta = Math.Min(beta, lowestScore);
if (beta <= alpha)
break;
deck.Add(((ComputerMove)move).Card);
}
bestMove.Score = lowestScore;
return bestMove;
}
// Iterative deepening minimax
private Move IterativeDeepening(State state, int timeLimit, Deck deck)
{
int depth = 1;
Stopwatch timer = new Stopwatch();
Move bestMove = null;
// start the search
timer.Start();
while (timer.ElapsedMilliseconds < timeLimit)
{
Tuple<Move, Boolean> result = RecursiveIterativeDeepening(state, depth, Double.MinValue, Double.MaxValue, timeLimit, timer, deck);
if (result.Item2) bestMove = result.Item1; // only update bestMove if full recursion
depth++;
}
return bestMove;
}
// adds a child node to the list of children
// after exploring a move - removes the move from untried
public Node AddChild(Move move, State state, Deck deck)
{
Node child = new Node(move, this, state, deck);
this.untriedMoves.Remove(move);
this.children.Add(child);
return child;
}
// Time limited MCTS
private Node TimeLimited(State rootState, int timeLimit, Stopwatch timer, Deck deck)
{
Node rootNode = new Node(null, null, rootState, deck);
while (true)
{
if (timer.ElapsedMilliseconds > timeLimit)
{
if (FindBestChild(rootNode.Children) == null && !rootNode.state.IsGameOver())
{
timeLimit += 10;
timer.Restart();
}
else
{
return rootNode;
}
}
Node node = rootNode;
State state = rootState.Clone();
Deck clonedDeck = deck.Clone();
// 1: Select
while (node.UntriedMoves.Count == 0 && node.Children.Count != 0)
{
node = node.SelectChild();
state = state.ApplyMove(node.GeneratingMove);
if (node.GeneratingMove is ComputerMove)
{
clonedDeck.Remove(((ComputerMove)node.GeneratingMove).Card);
if (clonedDeck.IsEmpty()) clonedDeck = new Deck();
}
}
// 2: Expand
if (node.UntriedMoves.Count != 0)
{
Move randomMove = node.UntriedMoves[random.Next(0, node.UntriedMoves.Count)];
if (randomMove is ComputerMove)
{
if (clonedDeck.IsEmpty()) clonedDeck = new Deck();
clonedDeck.Remove(((ComputerMove)randomMove).Card);
state = state.ApplyMove(randomMove);
node = node.AddChild(randomMove, state, clonedDeck);
}
else
{
state = state.ApplyMove(randomMove);
node = node.AddChild(randomMove, state, clonedDeck);
}
}
// 3: Simulation
while (state.GetMoves(clonedDeck).Count != 0)
{
Move move = state.GetRandomMove(clonedDeck);
if (move is ComputerMove)
{
if (clonedDeck.IsEmpty()) clonedDeck = new Deck();
clonedDeck.Remove(((ComputerMove)move).Card);
state = state.ApplyMove(move);
}
else
{
state = state.ApplyMove(move);
}
}
// 4: Backpropagation
while (node != null)
{
node.Update(state.GetResult());
node = node.Parent;
}
}
}
// Parallel time limited MCTS
private DIRECTION ParallelTimeLimitedMCTS(State currentState, int timeLimit, Deck deck)
{
ConcurrentBag<Node> allChildren = new ConcurrentBag<Node>();
int numOfChildren = currentState.GetMoves(deck).Count;
Stopwatch timer = new Stopwatch();
timer.Start();
Parallel.For(0, NUM_THREADS, i =>
{
Node resultRoot = TimeLimited(currentState, timeLimit, timer, deck);
foreach (Node child in resultRoot.Children)
{
allChildren.Add(child);
}
});
timer.Stop();
List<int> totalVisits = new List<int>(4) { 0, 0, 0, 0 };
List<double> totalResults = new List<double>(4) { 0, 0, 0, 0 };
foreach (Node child in allChildren)
{
int direction = (int)((PlayerMove)child.GeneratingMove).Direction;
totalVisits[direction] += child.Visits;
totalResults[direction] += child.Results;
}
double best = Double.MinValue;
int bestDirection = -1;
for (int k = 0; k < 4; k++)
{
double avg = totalResults[k] / totalVisits[k];
if (avg > best)
{
best = avg;
bestDirection = k;
}
}
if (bestDirection == -1) return (DIRECTION)(-1);
return (DIRECTION)bestDirection;
}
// Returns a random move
internal Move GetRandomMove(Deck deck)
{
List<Move> moves = GetMoves(deck);
int index = random.Next(0, moves.Count);
return moves[index];
}
public Deck(Deck deck)
{
this.cards = new List<int>(deck.cards);
}
// Classic Minimax using alpha-beta pruning
private Move MinimaxAlgorithm(State state, int depth, double alpha, double beta, Deck deck)
{
Move bestMove;
if (depth == 0 || state.IsGameOver())
{
if (state.Player == GameEngine.PLAYER)
{
bestMove = new PlayerMove(); // default constructor creates dummy action
bestMove.Score = AI.Evaluate(state);
return bestMove;
}
else if (state.Player == GameEngine.COMPUTER)
{
bestMove = new ComputerMove(); // default constructor creates dummy action
bestMove.Score = AI.Evaluate(state);
return bestMove;
}
else
{
throw new Exception();
}
}
if (state.Player == GameEngine.PLAYER)
return Max(state, depth, alpha, beta);
else
return Min(state, depth, alpha, beta);
}