/// <summary>
/// Expands a selected node, if possible.
/// </summary>
/// <param name="id">The selected node.</param>
/// <param name="tree">The game tree object.</param>
/// <returns></returns>
private static int Expand(int id, GameTree tree)
{
// Get the node object that corresponds with the input ID.
GameTreeNode node = tree.GetNode(id);
// If the node has at least one unplayed child, is not a dead end, and is not a goal state.
if (node.Unplayed.Count > 0 && !node.DeadEnd && !node.IsGoal)
{
// Choose an unplayed child at random.
GameTreeEdge outgoing = node.Unplayed.PickRandom <GameTreeEdge>();
// Remove the child from the list of unplayed edges.
node.Unplayed.Remove(outgoing);
// Create the node object and store the child's ID.
int child = tree.CreateNode(node.Domain, node.Problem, outgoing).ID;
// Save the parent node to disk.
tree.SetNode(node);
// Return the child ID.
return(child);
}
// Return the leaf node.
return(node.ID);
}
/// <summary>
/// The base constructor.
/// </summary>
/// <param name="domain">The base domain object.</param>
/// <param name="problem">The base problem object.</param>
/// <param name="path">The path used to save files to disk.</param>
public GameTree(Domain domain, Problem problem, string path)
{
// Store the domain, problem, and path.
this.domain = domain;
this.problem = problem;
this.path = path;
// Store the player's name.
player = problem.Player.ToLower();
// Get and store the NPC names.
npcs = GetNPCs();
// Establish the turn order.
turnOrder = GetTurnOrder();
// Create a new hashtable to store tree edges.
tree = new Hashtable();
// Initialize the session counters.
nodeCounter = 0;
totalPlays = 0;
lowestDepth = 0;
goalStateCount = 0;
deadEndCount = 0;
totalWins = 0;
totalLosses = 0;
// Create the tree's root node.
GameTreeNode root = CreateNode(domain, problem, null);
}
/// <summary>
/// Calculate and return the interval of the current node.
/// </summary>
/// <param name="node">The current node object.</param>
/// <returns></returns>
public double GetInterval(GameTreeNode node)
{
// If the node has been played before and is not a dead end.
if (node.TimesPlayed > 0 && !node.DeadEnd)
{
// Calculate and return the node's interval.
return(((double)node.Wins / (double)node.TimesPlayed) + Math.Sqrt((2 * Math.Log(TotalPlays)) / (double)node.TimesPlayed));
}
// Otherwise, return the error value.
return(-1);
}
/// <summary>
/// Creates a new node object.
/// </summary>
/// <param name="domain">The node's domain.</param>
/// <param name="problem">The node's problem.</param>
/// <param name="incoming">The node's incoming edge.</param>
/// <returns></returns>
public GameTreeNode CreateNode(Domain domain, Problem problem, GameTreeEdge incoming)
{
// Create a placeholder for the new node object.
GameTreeNode node = null;
// If the node is a root, initialize a root node.
if (incoming == null)
{
node = new GameTreeNode(domain, problem, 0);
}
// Otherwise, it is a child node...
else
{
// Store the current node's ID in the incoming edge.
incoming.Child = ++nodeCounter;
// Create the new node object.
node = new GameTreeNode(domain, problem, incoming, GetSuccessorState(incoming), incoming.Child, GetDepth(incoming.Parent) + 1);
// Add the edge to the tree hashtable.
tree.Add(incoming.Child, incoming.Parent);
}
// If the node is a goal state, iterate the goal state counter.
if (node.IsGoal)
{
goalStateCount++;
}
// If the node is at a lower depth than the previous record holder, update the depth counter.
if (node.Depth > lowestDepth)
{
lowestDepth = node.Depth;
}
// Find and store the node's outgoing edges.
node.Outgoing = GetOutgoingEdges(node, GetCurrentTurn(node));
// Iterate through the node's outgoing edges.
foreach (GameTreeEdge edge in node.Outgoing)
{
// And add each of them to the unplayed collection.
node.Unplayed.Add(edge);
}
// Save the current node to disk.
SetNode(node);
// Return the current node object.
return(node);
}
/// <summary>
/// Returns a list of outgoing edges for a given node.
/// </summary>
/// <param name="node">The node object.</param>
/// <param name="actor">The name of the current actor.</param>
/// <returns>A list of outgoing edges.</returns>
public List <GameTreeEdge> GetOutgoingEdges(GameTreeNode node, string actor)
{
// Initialize the list of outgoing edges.
List <GameTreeEdge> outgoing = new List <GameTreeEdge>();
// Iterate through the actions enabled for the input actor in the current node's state.
foreach (Operator action in StateSpaceTools.GetActions(actor, node.Domain, node.Problem, node.State))
{
// Add an outgoing edge for each of these actions to the list.
outgoing.Add(new GameTreeEdge(action, node.ID));
}
// Return the list of outgoing edges.
return(outgoing);
}
/// <summary>
/// Simulates a playout from the current node.
/// </summary>
/// <param name="id">The current node's ID.</param>
/// <returns>Whether the playout was won or lost.</returns>
public bool Simulate(int id)
{
// Read the node's object from disk.
GameTreeNode node = GetNode(id);
// Iterate the total plays.
totalPlays++;
// Initialize a dead end check.
bool check = false;
// If the node is not a dead end before it is played, we need to check.
if (!node.DeadEnd)
{
check = true;
}
// Play a game and store the result.
bool result = node.Play();
// Store a win.
if (result)
{
totalWins++;
}
// Otherwise, store a loss.
else
{
totalLosses++;
}
// If we found a new dead end, record it.
if (check && node.DeadEnd)
{
deadEndCount++;
}
// Save the node to disk.
SetNode(node);
// Return the result.
return(result);
}
/// <summary>
/// Selects a leaf node to expand.
/// </summary>
/// <param name="id">The ID of the current node.</param>
/// <param name="tree">The game tree object.</param>
/// <returns></returns>
private static int Select(int id, GameTree tree)
{
// Get the node object that corresponds to the current ID.
GameTreeNode node = tree.GetNode(id);
// If the node has not been played before, has at least one outgoing edge, is not a dead end, and is not a goal state...
if (node.Unplayed.Count == 0 && node.Outgoing.Count > 0 && !node.DeadEnd && !node.IsGoal)
{
// Create a variable to store the child with the highest interval.
int highestChild = -1;
// If it's not the player's turn...
if (!tree.TurnOrder[node.Depth % tree.TurnOrder.Count].Equals(tree.Player))
{
// Set the highest child to be the first child.
highestChild = node.Outgoing[0].Child;
// Loop through every remaining child.
for (int i = 1; i < node.Outgoing.Count; i++)
{
// If the current child has a higher interval than the stored child.
if (tree.GetInterval(node.Outgoing[i].Child) > tree.GetInterval(highestChild))
{
// Store the current child.
highestChild = node.Outgoing[i].Child;
}
}
}
// If it's the player's turn, chose an outgoing edge at random.
else
{
highestChild = node.Outgoing.PickRandom <GameTreeEdge>().Child;
}
// Recursively call this method with the selected child.
return(Select(highestChild, tree));
}
// Return the leaf node.
return(node.ID);
}
/// <summary>
/// Propagates a roll out's result back through the tree.
/// </summary>
/// <param name="result">Whether the roll out resulted in a win or loss.</param>
/// <param name="node">The current node.</param>
/// <param name="tree">The game tree object.</param>
private static void Propagate(bool result, int node, GameTree tree)
{
// Get the current node's parent ID.
int parent = tree.GetParent(node);
// Loop until we hit the root node's null parent link.
while (parent != -1)
{
// Get the parent's node object from the game tree.
GameTreeNode parentNode = tree.GetNode(parent);
// Add the win/loss to the parent's node object.
parentNode.AddResult(result);
// Save the parent's node object to disk.
tree.SetNode(parentNode);
// Set the parent ID to the grandparent ID.
parent = tree.GetParent(parent);
}
}
/// <summary>
/// Write a node object to disk.
/// </summary>
/// <param name="node">The node's ID.</param>
public void SetNode(GameTreeNode node)
{
// Given the path and ID, write the node object to disk.
BinarySerializer.SerializeObject <GameTreeNode>(path + node.ID, node);
}
/// <summary>
/// Get the current turn taker.
/// </summary>
/// <param name="node">The current node.</param>
/// <returns>The name of the character who gets to act.</returns>
private string GetCurrentTurn(GameTreeNode node)
{
// Returns the character who gets to act at this level.
return(turnOrder[node.Depth % turnOrder.Count]);
}
