private Assignment <Var, Val> Backtrack(CSP <Var, Val> csp, Assignment <Var, Val> assignment)
{
if (assignment.IsComplete(csp.Variables))
{
return(assignment);
}
Assignment <Var, Val> result = null;
var var = SelectUnassignedVariable(csp, assignment);
foreach (var value in OrderDomainValues(csp, assignment, var))
{
assignment.Add(var, value);
if (assignment.IsConsistent(csp.GetConstraints(var)))
{
var log = Inference(csp, assignment, var);
if (!log.IsConsistencyFound())
{
result = Backtrack(csp, assignment);
if (result != null)
{
break;
}
}
log.Undo(csp);
}
assignment.Remove(var);
}
return(result);
}
private static int CountLostValues(CSP <Var, Val> csp, Assignment <Var, Val> assignment, Var var, Val value)
{
var result = 0;
var assign = new Assignment <Var, Val>();
assign.Add(var, value);
foreach (var constraint in csp.GetConstraints(var))
{
if (constraint.GetScope().Count() == 2)
{
Var neighbor = csp.GetNeighbor(var, constraint);
if (!assignment.Contains(neighbor))
{
foreach (var val in csp.GetDomain(neighbor))
{
assign.Add(neighbor, val);
if (!constraint.IsSatisfiedWith(assign))
{
++result;
}
}
}
}
}
return(result);
}
public IEnumerable <Var> Apply(CSP <Var, Val> csp, IEnumerable <Var> vars)
{
var result = new List <Var>();
var maxDegree = -1;
foreach (var var in vars)
{
var degree = csp.GetConstraints(var).Count();
if (degree > maxDegree)
{
result.Clear();
maxDegree = degree;
}
if (degree == maxDegree)
{
result.Add(var);
}
}
return(result);
}
