Fixed Minimax search to use the new GameTreeNode, MinimaxProperty classes.

The previous implementation was overly complicated and may have been buggy except when searching only 2 plies ahead.

src/net/woodyfolsom/msproj/StateEvaluator.java

@@ -7,6 +7,10 @@ public class StateEvaluator {
 		this.gameConfig = gameConfig;
 	}
 	
+	public GameConfig getGameConfig() {
+		return gameConfig;
+	}
+	
 	public GameScore scoreGame(GameState gameState) {
 		GameBoard gameBoard;
 		if (gameState.getGameBoard().isTerritoryMarked()) {

src/net/woodyfolsom/msproj/policy/GameTreeNode.java

@@ -1,69 +0,0 @@
-package net.woodyfolsom.msproj.policy;
-
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Set;
-
-import net.woodyfolsom.msproj.Action;
-import net.woodyfolsom.msproj.GameState;
-
-public class GameTreeNode {
-	private GameState gameState;
-	private GameTreeNode parent;
-	private int numVisits;
-	private int numWins;
-	private Map<Action, GameTreeNode> children = new HashMap<Action, GameTreeNode>();
-
-	public GameTreeNode(GameState gameState) {
-		this.gameState = gameState;
-	}
-
-	public void addChild(Action action, GameTreeNode child) {
-		children.put(action, child);
-		child.parent = this;
-	}
-
-	public Set<Action> getActions() {
-		return children.keySet();
-	}
-
-	public GameTreeNode getChild(Action action) {
-		return children.get(action);
-	}
-
-	public int getNumChildren() {
-		return children.size();
-	}
-
-	public GameState getGameState() {
-		return gameState;
-	}
-
-	public int getNumVisits() {
-		return numVisits;
-	}
-
-	public int getNumWins() {
-		return numWins;
-	}
-	
-	public GameTreeNode getParent() {
-		return parent;
-	}
-
-	public boolean isRoot() {
-		return parent == null;
-	}
-
-	public boolean isTerminal() {
-		return children.size() == 0;
-	}
-
-	public void incrementVisits() {
-		numVisits++;
-	}
-
-	public void incrementWins() {
-		numWins++;
-	}
-}

src/net/woodyfolsom/msproj/policy/Minimax.java

@@ -1,77 +1,131 @@
 package net.woodyfolsom.msproj.policy;
 
-import java.util.ArrayList;
 import java.util.List;
 
 import net.woodyfolsom.msproj.Action;
 import net.woodyfolsom.msproj.GameConfig;
-import net.woodyfolsom.msproj.GameScore;
 import net.woodyfolsom.msproj.GameState;
 import net.woodyfolsom.msproj.GoGame;
 import net.woodyfolsom.msproj.Player;
 import net.woodyfolsom.msproj.StateEvaluator;
+import net.woodyfolsom.msproj.tree.GameTreeNode;
+import net.woodyfolsom.msproj.tree.MinimaxProperties;
 
 public class Minimax implements Policy {
-	private static final int DEFAULT_RECURSIVE_PLAYS = 1;
+	private static final int DEFAULT_LOOKAHEAD = 1;
 	
 	private final ValidMoveGenerator validMoveGenerator = new ValidMoveGenerator();
 
+	private int lookAhead;
+
+	public Minimax() {
+		this(DEFAULT_LOOKAHEAD);
+	}
+	
+	public Minimax(int lookAhead) {
+		this.lookAhead = lookAhead;
+	}
+	
 	@Override
 	public Action getAction(GameConfig gameConfig, GameState gameState,
-			Player color) {
+			Player player) {
-		MoveCandidate moveCandidate = findBestMinimaxResult(
-				DEFAULT_RECURSIVE_PLAYS * 2,
-				gameConfig, gameState, color, false, Action.PASS);
-
-		return moveCandidate.move;
-	}
-
-	private MoveCandidate findBestMinimaxResult(int recursionLevels,
-			GameConfig gameConfig, GameState gameState,
-			Player initialColor, boolean playAsOpponent, Action bestPrevMove) {
 		
 		StateEvaluator stateEvaluator = new StateEvaluator(gameConfig);
-		List<MoveCandidate> randomMoveCandidates = new ArrayList<MoveCandidate>();
 		
-		Player colorPlaying = GoGame.getColorToPlay(initialColor, playAsOpponent);
+		GameTreeNode<MinimaxProperties> rootNode = new GameTreeNode<MinimaxProperties>(gameState, new MinimaxProperties());
 		
-		List<Action> validMoves = validMoveGenerator.getActions(gameConfig,
+		if (player == Player.BLACK) {
-				gameState, colorPlaying, ActionGenerator.ALL_ACTIONS);
+			return getMax(
-		
+				lookAhead * 2,
-		for (Action randomMove : validMoves) {
+				stateEvaluator, 
-			GameState stateCopy = new GameState(gameState);
+				rootNode,
-			stateCopy.playStone(colorPlaying, randomMove);
+				player);
-			if (recursionLevels > 1) {
+		} else {
-				randomMoveCandidates.add(findBestMinimaxResult(recursionLevels - 1,
+			return getMin(
-						gameConfig, stateCopy, initialColor,
+					lookAhead * 2,
-						!playAsOpponent, randomMove));
+					stateEvaluator, 
-			} else {
+					rootNode,
-				GameScore score = stateEvaluator.scoreGame(stateCopy);
+					player);			
-				randomMoveCandidates.add(new MoveCandidate(randomMove, score));
-			}
-		}
-
-		// TODO use a sorted list and just return the last element
-		MoveCandidate bestMove = randomMoveCandidates.get(0);
-		double bestScoreSoFar = bestMove.score.getScore(colorPlaying);
-
-		for (MoveCandidate moveCandidate : randomMoveCandidates) {
-			if (moveCandidate.score.getScore(colorPlaying) > bestScoreSoFar) {
-				bestMove = moveCandidate;
-				bestScoreSoFar = moveCandidate.score.getScore(colorPlaying);
-			}
-		}
-
-		// Fix to prevent thinking that the _opponent's_ best move is the move
-		// to make.
-		// If evaluating an opponent's move, the best move (for my opponent) is
-		// my previous move which gives the opponent the highest score.
-		// This should only happen if recursionLevels is initially odd.
-		if (playAsOpponent) {
-			return new MoveCandidate(bestPrevMove, bestMove.score);
-		} else { // if evaluating my own move, the move which gives me the
-					// highest score is the best.
-			return bestMove;
 		}
 	}
+
+	private Action getMax(int recursionLevels,
+			StateEvaluator stateEvaluator,
+			GameTreeNode<MinimaxProperties> node,
+			Player player) {
+
+		GameState gameState = new GameState(node.getGameState());
+		
+		List<Action> validMoves = validMoveGenerator.getActions(stateEvaluator.getGameConfig(),
+				node.getGameState(), player, ActionGenerator.ALL_ACTIONS);
+		
+		for (Action nextMove : validMoves) {
+			GameState nextState = new GameState(gameState);
+			nextState.playStone(player, nextMove);
+			GameTreeNode<MinimaxProperties> childNode = new GameTreeNode<MinimaxProperties>(nextState, new MinimaxProperties());
+			node.addChild(nextMove, childNode);
+			if (recursionLevels > 1) {
+				getMin(recursionLevels - 1, stateEvaluator, childNode, GoGame.getColorToPlay(player, true));
+			} else {
+				//tail condition - set reward of this leaf node
+				childNode.getProperties().setReward(stateEvaluator.scoreGame(nextState).getAggregateScore());
+			}
+		}
+		
+		double maxScore = Double.NEGATIVE_INFINITY;
+		Action bestAction = Action.NONE;
+		
+		for (Action nextMove : validMoves) {
+			GameTreeNode<MinimaxProperties> childNode = node.getChild(nextMove);
+			double gameScore = childNode.getProperties().getReward();
+			
+			if (gameScore > maxScore) {
+				maxScore = gameScore;
+				bestAction = nextMove;
+			}
+		}
+		
+		node.getProperties().setReward(maxScore);
+		return bestAction;
+	}
+	
+	private Action getMin(int recursionLevels,
+			StateEvaluator stateEvaluator,
+			GameTreeNode<MinimaxProperties> node,
+			Player player) {
+
+		GameState gameState = new GameState(node.getGameState());
+		
+		List<Action> validMoves = validMoveGenerator.getActions(stateEvaluator.getGameConfig(),
+				node.getGameState(), player, ActionGenerator.ALL_ACTIONS);
+		
+		for (Action nextMove : validMoves) {
+			GameState nextState = new GameState(gameState);
+			nextState.playStone(player, nextMove);
+			GameTreeNode<MinimaxProperties> childNode = new GameTreeNode<MinimaxProperties>(nextState, new MinimaxProperties());
+			node.addChild(nextMove, childNode);
+			if (recursionLevels > 1) {
+				getMax(recursionLevels - 1, stateEvaluator, childNode, GoGame.getColorToPlay(player, true));
+			} else {
+				//tail condition - set reward of this leaf node
+				childNode.getProperties().setReward(stateEvaluator.scoreGame(nextState).getAggregateScore());
+			}
+		}
+		
+		double minScore = Double.POSITIVE_INFINITY;
+		Action bestAction = Action.NONE;
+		
+		for (Action nextMove : validMoves) {
+			GameTreeNode<MinimaxProperties> childNode = node.getChild(nextMove);
+			double gameScore = childNode.getProperties().getReward();
+			
+			if (gameScore < minScore) {
+				minScore = gameScore;
+				bestAction = nextMove;
+			}
+		}
+		
+		node.getProperties().setReward(minScore);
+		return bestAction;
+	}
 }

src/net/woodyfolsom/msproj/policy/MonteCarlo.java

@@ -7,6 +7,8 @@ import net.woodyfolsom.msproj.Action;
 import net.woodyfolsom.msproj.GameConfig;
 import net.woodyfolsom.msproj.GameState;
 import net.woodyfolsom.msproj.Player;
+import net.woodyfolsom.msproj.tree.GameTreeNode;
+import net.woodyfolsom.msproj.tree.MonteCarloProperties;
 
 public abstract class MonteCarlo implements Policy {
 	protected Policy movePolicy;
@@ -24,7 +26,7 @@ public abstract class MonteCarlo implements Policy {
 	 * @param node
 	 * @return
 	 */
-	public abstract List<GameTreeNode> descend(GameTreeNode node);
+	public abstract List<GameTreeNode<MonteCarloProperties>> descend(GameTreeNode<MonteCarloProperties> node);
 	
 	@Override
 	public Action getAction(GameConfig gameConfig, GameState gameState,
@@ -35,20 +37,20 @@ public abstract class MonteCarlo implements Policy {
 		//Note that this may lose the game by forfeit even when picking any random move could
 		//result in a win.
 		
-		GameTreeNode rootNode = new GameTreeNode(gameState);
+		GameTreeNode<MonteCarloProperties> rootNode = new GameTreeNode<MonteCarloProperties>(gameState, new MonteCarloProperties());
 		
 		do {
 			//TODO these return types may need to be lists for some MC methods
-			List<GameTreeNode> selectedNodes = descend(rootNode);
+			List<GameTreeNode<MonteCarloProperties>> selectedNodes = descend(rootNode);
-			List<GameTreeNode> newLeaves = new ArrayList<GameTreeNode>();
+			List<GameTreeNode<MonteCarloProperties>> newLeaves = new ArrayList<GameTreeNode<MonteCarloProperties>>();
 			
-			for (GameTreeNode selectedNode: selectedNodes) {
+			for (GameTreeNode<MonteCarloProperties> selectedNode: selectedNodes) {
-				for (GameTreeNode newLeaf : grow(selectedNode)) {
+				for (GameTreeNode<MonteCarloProperties> newLeaf : grow(selectedNode)) {
 					newLeaves.add(newLeaf);
 				}
 			}
 			
-			for (GameTreeNode newLeaf : newLeaves) {
+			for (GameTreeNode<MonteCarloProperties> newLeaf : newLeaves) {
 				int reward = rollout(newLeaf);
 				update(newLeaf, reward);
 			}
@@ -63,13 +65,13 @@ public abstract class MonteCarlo implements Policy {
 		return elapsedTime;
 	}
 	
-	public abstract Action getBestAction(GameTreeNode node);
+	public abstract Action getBestAction(GameTreeNode<MonteCarloProperties> node);
 	
-	public abstract List<GameTreeNode> grow(GameTreeNode node);
+	public abstract List<GameTreeNode<MonteCarloProperties>> grow(GameTreeNode<MonteCarloProperties> node);
 	
-	public abstract int rollout(GameTreeNode node);
+	public abstract int rollout(GameTreeNode<MonteCarloProperties> node);
 	
-	public abstract void update(GameTreeNode node, int reward);
+	public abstract void update(GameTreeNode<MonteCarloProperties> node, int reward);
 	
 	public long getSearchTimeLimit() {
 		return searchTimeLimit;

src/net/woodyfolsom/msproj/policy/MonteCarloUCT.java

@@ -4,6 +4,8 @@ import java.util.ArrayList;
 import java.util.List;
 
 import net.woodyfolsom.msproj.Action;
+import net.woodyfolsom.msproj.tree.GameTreeNode;
+import net.woodyfolsom.msproj.tree.MonteCarloProperties;
 
 public class MonteCarloUCT extends MonteCarlo {
 	
@@ -12,17 +14,20 @@ public class MonteCarloUCT extends MonteCarlo {
 	}
 
 	@Override
-	public List<GameTreeNode> descend(GameTreeNode node) {
+	public List<GameTreeNode<MonteCarloProperties>> descend(GameTreeNode<MonteCarloProperties> node) {
-		double bestScore = (double) node.getNumWins() / node.getNumVisits();
+		double bestScore = Double.NEGATIVE_INFINITY;
-		GameTreeNode bestNode = node;
+		GameTreeNode<MonteCarloProperties> bestNode = node;
 		
 		//This appears slightly redundant with getBestAction() but it is not -
 		//descend() may pick the current node rather than a child to expand (if a child has a good score but high/low uncertainty)
 		//but getBestAction specifically asks for the optimum action to take from the current node,
 		//even if it results in a worse next state.
 		for (Action action : node.getActions()) {
-			GameTreeNode childNode = node.getChild(action);
+			GameTreeNode<MonteCarloProperties> childNode = node.getChild(action);
-			double childScore = (double) childNode.getNumWins() / childNode.getNumVisits();
+			
+			MonteCarloProperties properties = childNode.getProperties();
+			double childScore = (double) properties.getWins() / properties.getVisits();
+			
 			if (childScore >= bestScore) {
 				bestScore = childScore;
 				bestNode = childNode;
@@ -30,7 +35,7 @@ public class MonteCarloUCT extends MonteCarlo {
 		}
 		
 		if (bestNode == node) {
-			List<GameTreeNode> bestNodeList = new ArrayList<GameTreeNode>();
+			List<GameTreeNode<MonteCarloProperties>> bestNodeList = new ArrayList<GameTreeNode<MonteCarloProperties>>();
 			bestNodeList.add(bestNode);
 			return bestNodeList;
 		} else {
@@ -39,13 +44,16 @@ public class MonteCarloUCT extends MonteCarlo {
 	}
 
 	@Override
-	public Action getBestAction(GameTreeNode node) {
+	public Action getBestAction(GameTreeNode<MonteCarloProperties> node) {
 		Action bestAction = Action.NONE;
 		double bestScore = Double.NEGATIVE_INFINITY;
 		
 		for (Action action : node.getActions()) {
-			GameTreeNode childNode = node.getChild(action);
+			GameTreeNode<MonteCarloProperties> childNode = node.getChild(action);
-			double childScore = (double) childNode.getNumWins() / childNode.getNumVisits();
+			
+			MonteCarloProperties properties = childNode.getProperties();
+			double childScore = (double) properties.getWins() / properties.getVisits();
+			
 			if (childScore >= bestScore) {
 				bestScore = childScore;
 				bestAction = action;
@@ -56,19 +64,19 @@ public class MonteCarloUCT extends MonteCarlo {
 	}
 
 	@Override
-	public List<GameTreeNode> grow(GameTreeNode node) {
+	public List<GameTreeNode<MonteCarloProperties>> grow(GameTreeNode<MonteCarloProperties> node) {
 		// TODO Auto-generated method stub
 		return null;
 	}
 
 	@Override
-	public int rollout(GameTreeNode node) {
+	public int rollout(GameTreeNode<MonteCarloProperties> node) {
 		// TODO Auto-generated method stub
 		return 0;
 	}
 
 	@Override
-	public void update(GameTreeNode node, int reward) {
+	public void update(GameTreeNode<MonteCarloProperties> node, int reward) {
 		// TODO Auto-generated method stub
 		
 	}

src/net/woodyfolsom/msproj/policy/MoveCandidate.java

@@ -1,14 +0,0 @@
-package net.woodyfolsom.msproj.policy;
-
-import net.woodyfolsom.msproj.Action;
-import net.woodyfolsom.msproj.GameScore;
-
-public class MoveCandidate {
-	public final Action move;
-	public final GameScore score;
-
-	public MoveCandidate(Action move, GameScore score) {
-		this.move = move;
-		this.score = score;
-	}
-}

src/net/woodyfolsom/msproj/tree/AlphaBetaPropeties.java

@@ -0,0 +1,18 @@
+package net.woodyfolsom.msproj.tree;
+
+public class AlphaBetaPropeties extends GameTreeNodeProperties{
+	int alpha = 0;
+	int beta = 0;
+	public int getAlpha() {
+		return alpha;
+	}
+	public void setAlpha(int alpha) {
+		this.alpha = alpha;
+	}
+	public int getBeta() {
+		return beta;
+	}
+	public void setBeta(int beta) {
+		this.beta = beta;
+	}
+}

src/net/woodyfolsom/msproj/tree/GameTreeNode.java

@@ -0,0 +1,57 @@
+package net.woodyfolsom.msproj.tree;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+import net.woodyfolsom.msproj.Action;
+import net.woodyfolsom.msproj.GameState;
+
+public class GameTreeNode<T extends GameTreeNodeProperties> {
+	private GameState gameState;
+	private GameTreeNode<T> parent;
+	private Map<Action, GameTreeNode<T>> children = new HashMap<Action, GameTreeNode<T>>();
+	private T properties;
+
+	public GameTreeNode(GameState gameState, T properties) {
+		this.gameState = gameState;
+		this.properties = properties;
+	}
+
+	public void addChild(Action action, GameTreeNode<T> child) {
+		children.put(action, child);
+		child.parent = this;
+	}
+
+	public Set<Action> getActions() {
+		return children.keySet();
+	}
+
+	public GameTreeNode<T> getChild(Action action) {
+		return children.get(action);
+	}
+
+	public int getNumChildren() {
+		return children.size();
+	}
+
+	public GameState getGameState() {
+		return gameState;
+	}
+	
+	public GameTreeNode<T> getParent() {
+		return parent;
+	}
+
+	public T getProperties() {
+		return properties;
+	}
+	
+	public boolean isRoot() {
+		return parent == null;
+	}
+
+	public boolean isTerminal() {
+		return children.size() == 0;
+	}
+}

src/net/woodyfolsom/msproj/tree/GameTreeNodeProperties.java

@@ -0,0 +1,5 @@
+package net.woodyfolsom.msproj.tree;
+
+public abstract class GameTreeNodeProperties {
+
+}

src/net/woodyfolsom/msproj/tree/MinimaxProperties.java

@@ -0,0 +1,13 @@
+package net.woodyfolsom.msproj.tree;
+
+public class MinimaxProperties extends GameTreeNodeProperties {
+	private double reward = 0.0;
+
+	public double getReward() {
+		return reward;
+	}
+
+	public void setReward(double reward) {
+		this.reward = reward;
+	}
+}

src/net/woodyfolsom/msproj/tree/MonteCarloProperties.java

@@ -0,0 +1,18 @@
+package net.woodyfolsom.msproj.tree;
+
+public class MonteCarloProperties extends GameTreeNodeProperties {
+	int visits = 0;
+	int wins = 0;
+	public int getVisits() {
+		return visits;
+	}
+	public void setVisits(int visits) {
+		this.visits = visits;
+	}
+	public int getWins() {
+		return wins;
+	}
+	public void setWins(int wins) {
+		this.wins = wins;
+	}
+}

test/net/woodyfolsom/msproj/policy/MinimaxTest.java

@@ -24,7 +24,7 @@ public class MinimaxTest {
 		System.out.println(gameState);
 
 		System.out.println("Generated move: " + move);
-		assertEquals("Expected B3 but was: " + move, "B3", move);
+		assertEquals("Expected B3 but was: " + move, Action.getInstance("B3"), move);
 		gameState.playStone(Player.WHITE, move);
 
 		System.out.println(gameState);
@@ -45,7 +45,7 @@ public class MinimaxTest {
 		System.out.println(gameState);
 
 		System.out.println("Generated move: " + move);
-		assertEquals("Expected B3 but was: " + move, "B3", move);
+		assertEquals("Expected B3 but was: " + move, Action.getInstance("B3"), move);
 		gameState.playStone(Player.BLACK, move);
 
 		System.out.println(gameState);