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Node.cs
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Node.cs
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public class Node
{
private static readonly Random random = new Random();
private TTTGameState state;
private TicState playingAs;
private Node? parent;
private List<Node> children;
private BoardLoc? moveMade;
private int visits;
private int misses;
private int wins;
public Node(TTTGameState state, TicState playingAs)
{
this.state = state;
this.playingAs = playingAs;
children = new List<Node>();
visits = 0;
misses = 0;
wins = 0;
}
public Node(Node parent, TTTGameState state, TicState playingAs, BoardLoc moveMade) : this(state, playingAs)
{
this.parent = parent;
this.moveMade = moveMade;
}
private Node bestUTC()
{
Node bestChild = children[0];
double bestUCTValue = double.NegativeInfinity;
double explorationFactor = Math.Sqrt(2);
foreach (Node child in children)
{
double exploitation = Math.Abs(child.wins) / (child.visits + double.Epsilon);
double exploration = explorationFactor * Math.Sqrt(Math.Log(visits) / (child.visits + double.Epsilon));
double uctValue = exploitation + exploration;
if (uctValue > bestUCTValue)
{
bestChild = child;
bestUCTValue = uctValue;
}
}
return bestChild;
}
private void Expand()
{
List<BoardLoc> legalMoves = state.GetLegalMoves();
foreach (BoardLoc move in legalMoves)
{
TTTGameState newState = state.MakeMove(move);
Node childNode = new Node(this, newState, playingAs, move);
children.Add(childNode);
}
}
public Node Traverse()
{
Node node = this;
Node? bestChild = null;
while (node.children.Count != 0)
{
bestChild = node.bestUTC();
node = bestChild;
}
if (node.state.GetBoardState() != TicState.N) return node;
node.Expand();
return node.children[random.Next(node.children.Count)];
}
public int Rollout()
{
TTTGameState currentState = new TTTGameState(state);
while (true)
{
if (currentState.GetBoardState() != TicState.N) break;
List<BoardLoc> moves = currentState.GetLegalMoves();
if (moves.Count == 0) break;
currentState = currentState.MakeMove(moves[random.Next(moves.Count)]);
}
if(currentState.GetBoardState() == playingAs) return 1;
if(currentState.GetBoardState() == TicState.T) return 0;
return -1;
}
public void Backpropagate(int result)
{
if(result>0) wins += result;
if(result<0) misses += result;
visits++;
if (parent == null) return;
parent.Backpropagate(result);
}
public BoardLoc GetBestMove()
{
Node bestNode = children[0];
double bestScore = bestNode.visits;
for (int index = 1; index < children.Count; index++)
{
Node nodeOn = children[index];
if (nodeOn.visits > bestScore)
{
bestNode = nodeOn;
bestScore = nodeOn.visits;
}
}
return bestNode.moveMade;
}
}