/**
* Constructs a node with the specified state, parent, action, and path
* cost.
*
* @param state
* the state in the state space to which the node corresponds.
* @param parent
* the node in the search tree that generated the node.
* @param action
* the action that was applied to the parent to generate the
* node.
* @param pathCost
* full pathCost from the root node to here, typically
* the root's path costs plus the step costs for executing
* the the specified action.
*/
public Node(System.Object state, Node parent, Action action, double stepCost)
: this(state)
{
this.parent = parent;
this.action = action;
this.pathCost = parent.pathCost + stepCost;
}
/**
* Inserts the node at the tail of the frontier if the corresponding state
* was not yet explored.
*/
protected override void addToFrontier(Node node)
{
if (!explored.Contains(node.getState()))
{
frontier.Enqueue(node);
updateMetrics(frontier.Count);
}
}
/**
* Calls the goal test of the problem and - if the goal test is effectively
* a {@link SolutionChecker} - additionally checks, whether the solution is
* acceptable. Solution checkers can be used to analyze several or all
* solutions with only one search run.
*/
public static bool isGoalState(Problem p, Node n)
{
bool isGoal = false;
GoalTest gt = p.getGoalTest();
if (gt.isGoalState(n.getState()))
{
if (gt is SolutionChecker)
{
isGoal = ((SolutionChecker)gt).isAcceptableSolution(
getSequenceOfActions(n), n.getState());
}
else
{
isGoal = true;
}
}
return isGoal;
}
/**
* Returns the children obtained from expanding the specified node in the
* specified problem.
*
* @param node
* the node to expand
* @param problem
* the problem the specified node is within.
*
* @return the children obtained from expanding the specified node in the
* specified problem.
*/
public List<Node> expand(Node node, Problem problem)
{
List<Node> successors = new List<Node>();
ActionsFunction actionsFunction = problem.getActionsFunction();
ResultFunction resultFunction = problem.getResultFunction();
StepCostFunction stepCostFunction = problem.getStepCostFunction();
foreach (Action action in actionsFunction.actions(node.getState()))
{
System.Object successorState = resultFunction.result(node.getState(), action);
double stepCost = stepCostFunction.c(node.getState(), action, successorState);
successors.Add(createNode(successorState, node, action, stepCost));
}
foreach (NodeListener listener in nodeListeners)
{
listener.onNodeExpanded(node);
}
counter++;
return successors;
}
/**
* Returns the list of actions corresponding to the complete path to the
* given node or NoOp if path length is one.
*/
public static List<Action> getSequenceOfActions(Node node)
{
List<Node> nodes = node.getPathFromRoot();
List<Action> actions = new List<Action>();
if(nodes.Count == 1)
{
// I'm at the root node, this indicates I started at the
// Goal node, therefore just return a NoOp
actions.Add(NoOpAction.NO_OP);
}
else
{
// ignore the root node this has no action
// hence index starts from 1 not zero
for (int i = 1; i < nodes.Count; i++)
{
Node node_temp = nodes[i];
actions.Add(node_temp.getAction());
}
}
return actions;
}
/**
* Computes the path cost for getting from the root node state via the
* parent node state to the specified state, creates a new node for the
* specified state, adds it as child of the provided parent, and returns it.
*/
public Node createNode(System.Object state, Node parent, Action action, double stepCost)
{
return new Node(state, parent, action, parent.getPathCost() + stepCost);
}
/**
* Inserts the node at the tail of the frontier.
*/
protected override void addToFrontier(Node node)
{
frontier.Enqueue(node);
updateMetrics(frontier.Count);
}
/**
*
* @param n
* @return the cost, traditionally denoted by g(n), of the path from the
* initial state to the node, as indicated by the parent pointers.
*/
public double g(Node n)
{
return n.getPathCost();
}