public Node(
string state,
Node parent,
MoveToAction action,
int stepCost,
int estimate
)
{
m_state = state;
m_parent = parent;
m_action = action;
m_pathCost = parent.PathCost + stepCost;
m_estimateCost = estimate;
}
public virtual IEnumerable<MoveToAction> Search( Problem problem )
{
List<Node> frontier = new List<Node>();
HashSet<Node> explored = new HashSet<Node>();
Node root = new Node( problem.InitialState );
frontier.Add( root );
while( frontier.Count > 0 ) {
Node nodeToExpand = frontier.First();
frontier.Remove( nodeToExpand );
//Console.WriteLine( nodeToExpand.State );
var newNodes = ExpandNode(
nodeToExpand,
explored,
problem
);
foreach( Node fn in newNodes ) {
var test = fn.Equals( newNodes.First() );
if( IsGoalState( fn.State, problem.GoalTest ) ) {
return ActionsFromNodes( fn.GetPathFromRoot() );
}
frontier.Add( fn );
}
// This could be costly. Find better alternative later
frontier = frontier
.OrderByDescending( n => n.PathCost + n.EstimateCost )
.Distinct()
.ToList();
}
return new List<MoveToAction>();
}
private IEnumerable<Node> ExpandNode(
Node node,
HashSet<Node> explored,
Problem problem
)
{
explored.Add( node );
var childNodes = new List<Node>();
var actionsFunction = problem.ActionsFunction;
var resultFunction = problem.ResultFunction;
var stepCostFunction = problem.StepCostFunction;
foreach( var action in actionsFunction.GetActions( node.State ) ) {
string successorState = resultFunction.Result(
node.State,
action
);
int stepCost = stepCostFunction.Cost(
node.State,
action,
successorState
);
int estimateCost = m_heuristic.Calculate( successorState );
var child = new Node(
successorState,
node,
action,
stepCost,
estimateCost
);
if( !explored.Contains( child ) ) {
childNodes.Add( child );
}
}
return childNodes;
}
public bool Equals( Node n )
{
if( ( object )n == null ) {
return false;
}
return m_state == n.State;
}