private IEnumerable <Dictionary <TK, TD> > Ac3Search(CspProblem <TK, TD> problem)
{
NodesVisited = 0L;
SolutionCount = 0L;
foreach (var assignment in Search())
{
yield return(assignment);
}
IEnumerable <Dictionary <TK, TD> > Search()
{
if (problem.Complete)
{
SolutionCount++;
yield return(problem.Assignment);
}
else
{
var variable = problem.NextUnassigned(SelectVariableHeuristic);
foreach (var value in variable.OrderDomainValues(OrderDomainHeuristic))
{
NodesVisited++;
variable.Value = value;
if (variable.Consistent)
{
var removals = Ac3(problem, out var isConsistent);
if (isConsistent)
{
// try finding solution
foreach (var solution in Search().Where(s => s is not null))
{
yield return(solution);
}
}
foreach (var(v, removalCount) in removals)
{
v.RestorePreviousDomain(removalCount - 1);
}
}
variable.Assigned = false;
}
yield return(null);
}
}
}
private IEnumerable <Dictionary <TK, TD> > ForwardCheckingSearch(CspProblem <TK, TD> problem)
{
NodesVisited = 0L;
SolutionCount = 0L;
foreach (var assignment in Search())
{
yield return(assignment);
}
IEnumerable <Dictionary <TK, TD> > Search()
{
if (problem.Complete)
{
SolutionCount++;
yield return(problem.Assignment);
}
else
{
var variable = problem.NextUnassigned(SelectVariableHeuristic);
foreach (var value in variable.OrderDomainValues(OrderDomainHeuristic))
{
NodesVisited++;
variable.Value = value;
if (variable.Consistent)
{
var emptyDomainFound = false;
var removals = new List <Variable <TK, TD> >();
// forward checking ->
// remove from Variables connected by constraints
// the values that are inconsistent with selected value
foreach (var v in variable.Constraints
.Where(c => !c.VariableTwo.Assigned)
.Select(c => c.VariableTwo))
{
var toRemove = v.Domain.Where(d => !v.CheckConsistency(d)).ToArray();
if (!toRemove.Any())
{
continue;
}
v.RemoveFromDomain(toRemove);
removals.Add(v);
if (v.Domain.Any())
{
continue;
}
emptyDomainFound = true;
break;
}
if (emptyDomainFound)
{
yield return(null);
}
else
{
// try finding solution
foreach (var solution in Search().Where(s => s is not null))
{
yield return(solution);
}
}
// restore domains to previous state
foreach (var v in removals)
{
v.RestorePreviousDomain();
}
}
variable.Assigned = false;
}
yield return(null);
}
}
}
