private async Task <Assignment <Tval> > Backtrack(ConstraintSatisfactionProblem <Tval> csp, Assignment <Tval> assignment)
{
if (assignment.IsComplete(csp.GetVariables()))
{
return(assignment);
}
Variable <Tval> variable = variableSelectionStrategy.SelectUnassignedVariable(csp, assignment);
foreach (Tval value in domainValueSelectionStragety.getOrderedDomainValues(variable, assignment, csp))
{
assignment.Assign(variable, value);
OnVariableAssigned(variable, value);
InferenceResults <Tval> inference = new InferenceResults <Tval>();
inference.StoreDomainForVariable(variable, variable.GetDomain());
variable.UpdateDomain(new Domain <Tval>(value));
// it should already be consistent if it reached this point
// since we make a pre-solving inference
//bool isConsistent = assignment.IsConsistent(csp.GetAllDiffConstraints());
//if (isConsistent)
if (true)
{
inference = await inferenceStrategy.Infer(csp, variable, value, inference);
if (inference.IsAssignmentConsistent())
{
Assignment <Tval> result = await Backtrack(csp, assignment);
if (result != null)
{
return(result);
}
}
}
assignment.RemoveAssignment(variable);
OnAssignmentRemoved(variable, value);
inference.RestoreOldDomains();
}
return(null);
}
public override async Task <Assignment <Tval> > Solve(ConstraintSatisfactionProblem <Tval> csp, Assignment <Tval> initialAssignment = null)
{
initialAssignment = initialAssignment ?? new Assignment <Tval>();
InferenceResults <Tval> preliminaryResults = await inferenceStrategy.Infer(csp);
if (preliminaryResults.IsAssignmentConsistent())
{
Assignment <Tval> solution = await Backtrack(csp, initialAssignment);
if (solution != null)
{
OnSolutionFound(solution);
return(solution);
}
}
OnNoSolutionFound();
return(null);
}
// we assume that, if the variable has already been assigned,
// the old value of the variable has been removed
// by an inference at a previous step, and therefore it is not
// present in the domain of its neighbours, but since we might
// have another variable that has the same value in its neighbour
// (the assignment was not consistent) there is going to be another
// inference to rule out inconsistent domains.
public override async Task <InferenceResults <Tval> > UpdateVariable(ConstraintSatisfactionProblem <Tval> csp, Assignment <Tval> assignment, Variable <Tval> variable, Tval value)
{
if (csp == null)
{
throw new ArgumentNullException("csp");
}
if (assignment == null)
{
throw new ArgumentNullException("assignment");
}
if (variable == null)
{
throw new ArgumentNullException("variable");
}
InferenceResults <Tval> removeInference = await RemoveVariable(csp, assignment, variable);
assignment.Assign(variable, value);
variable.UpdateDomain(new Domain <Tval>(value));
return(await inferenceStrategy.Infer(csp, variable, value, removeInference, false));
}
