public AStar(
ISearchProblem <TState, TAction> problem,
Func <string, string, double> heuristic) : base(problem)
{
_heuristic = heuristic;
var root = new HeuristicNode <TState, TAction>(Problem.Initial, Problem.InitialNode);
root.HeuristicPathCost = _heuristic(root.State.Name, Problem.Goal.Name);
_frontier = new List <HeuristicNode <TState, TAction> > {
root
};
}
private PathResult RbFs(HeuristicNode <TState, TAction> node, double limit)
{
Iterations++;
if (Problem.GoalTest(node.State))
{
return(new PathResult(node, node.HeuristicPathCost));
}
var successors = node.Expand(Problem).Select(HeuristicNode <TState, TAction> .From).ToList();
if (!successors.Any())
{
return(new PathResult(new None <HeuristicNode <TState, TAction> >(), double.PositiveInfinity));
}
foreach (var childNode in successors)
{
var childHCost = childNode.PathCost + _heuristic(childNode.State.Name, Problem.Goal.Name);
childNode.HeuristicPathCost = Math.Max(childHCost, node.HeuristicPathCost);
}
while (true)
{
successors.Sort();
var best = successors.FirstOrNone();
if (best.IsNone)
{
return(new PathResult(new None <HeuristicNode <TState, TAction> >(), double.PositiveInfinity));
}
if (best.Reduce().HeuristicPathCost > limit)
{
return(new PathResult(new None <HeuristicNode <TState, TAction> >(), best.Reduce().HeuristicPathCost));
}
var alternativeCost = successors.Count() > 1 ?
successors.ElementAt(1).HeuristicPathCost :
double.PositiveInfinity;
var res = RbFs(best.Reduce(), Math.Min(limit, alternativeCost));
best.Reduce().HeuristicPathCost = res.Cost;
if (!res.Node.IsNone)
{
return(new PathResult(res.Node, best.Reduce().HeuristicPathCost));
}
}
}
public override SearchExitCode Search()
{
Iterations = 0;
var root = new HeuristicNode <TState, TAction>(Problem.Initial, Problem.InitialNode);
root.HeuristicPathCost = _heuristic(root.State.Name, Problem.Goal.Name);
var res = RbFs(root, double.PositiveInfinity);
if (res.Node.IsNone)
{
return(SearchExitCode.Failure);
}
Solution = res.Node.Reduce().Path();
return(SearchExitCode.Success);
}
private void AddToFrontier(HeuristicNode <TState, TAction> node)
{
node.HeuristicPathCost = node.PathCost + _heuristic(node.State.Name, Problem.Goal.Name);
_frontier.Add(node);
_frontier.Sort();
}
