/**
* Establishes arc-consistency for (xi, xj).
* @return value true if the domain of xi was reduced.
*/
private bool makeArcConsistent(VAR xi, VAR xj, IConstraint <VAR, VAL> constraint, CSP <VAR, VAL> csp)
{
Domain <VAL> currDomain = csp.getDomain(xi);
ICollection <VAL> newValues = CollectionFactory.CreateQueue <VAL>();
Assignment <VAR, VAL> assignment = new Assignment <VAR, VAL>();
foreach (VAL vi in currDomain)
{
assignment.add(xi, vi);
foreach (VAL vj in csp.getDomain(xj))
{
assignment.add(xj, vj);
if (constraint.isSatisfiedWith(assignment))
{
newValues.Add(vi);
break;
}
}
}
if (newValues.Size() < currDomain.size())
{
csp.setDomain(xi, new Domain <VAL>(newValues));
return(true);
}
return(false);
}
/**
* Ignores constraints which are not binary.
*/
private int countLostValues(CSP <VAR, VAL> csp, Assignment <VAR, VAL> assignment, VAR var, VAL value)
{
int result = 0;
Assignment <VAR, VAL> assign = new Assignment <VAR, VAL>();
assign.add(var, value);
foreach (IConstraint <VAR, VAL> constraint in csp.getConstraints(var))
{
if (constraint.getScope().Size() == 2)
{
VAR neighbor = csp.getNeighbor(var, constraint);
if (!assignment.contains(neighbor))
{
foreach (VAL nValue in csp.getDomain(neighbor))
{
assign.add(neighbor, nValue);
if (!constraint.isSatisfiedWith(assign))
{
++result;
}
}
}
}
}
return(result);
}
public override Assignment <VAR, VAL> solve(CSP <VAR, VAL> csp)
{
Assignment <VAR, VAL> assignment = new Assignment <VAR, VAL>();
// Select a root from the List of Variables
VAR root = _useRandom ? Util.selectRandomlyFromList(csp.getVariables()) : csp.getVariables().Get(0);
// Sort the variables in topological order
ICollection <VAR> orderedVars = CollectionFactory.CreateQueue <VAR>();
IMap <VAR, IConstraint <VAR, VAL> > parentConstraints = CollectionFactory.CreateInsertionOrderedMap <VAR, IConstraint <VAR, VAL> >();
topologicalSort(csp, root, orderedVars, parentConstraints);
if (csp.getDomain(root).isEmpty())
{
return(null); // CSP has no solution! (needed if orderedVars.size() == 1)
}
// Establish arc consistency from top to bottom (starting at the bottom).
csp = csp.copyDomains(); // do not change the original CSP!
for (int i = orderedVars.Size() - 1; i > 0; i--)
{
VAR var = orderedVars.Get(i);
IConstraint <VAR, VAL> constraint = parentConstraints.Get(var);
VAR parent = csp.getNeighbor(var, constraint);
if (makeArcConsistent(parent, var, constraint, csp))
{
fireStateChanged(csp, null, parent);
if (csp.getDomain(parent).isEmpty())
{
return(null); // CSP has no solution!
}
}
}
// Assign values to variables from top to bottom.
for (int i = 0; i < orderedVars.Size(); ++i)
{
VAR var = orderedVars.Get(i);
foreach (VAL value in csp.getDomain(var))
{
assignment.add(var, value);
if (assignment.isConsistent(csp.getConstraints(var)))
{
fireStateChanged(csp, assignment, var);
break;
}
}
}
return(assignment);
}
/**
* Primitive operation, ordering the domain values of the specified variable.
*/
protected override IEnumerable <VAL> orderDomainValues(CSP <VAR, VAL> csp, Assignment <VAR, VAL> assignment, VAR var)
{
if (valSelectionStrategy != null)
{
return(valSelectionStrategy.apply(csp, assignment, var));
}
else
{
return(csp.getDomain(var));
}
}
private Assignment <VAR, VAL> generateRandomAssignment(CSP <VAR, VAL> csp)
{
Assignment <VAR, VAL> result = new Assignment <VAR, VAL>();
foreach (VAR var in csp.getVariables())
{
VAL randomValue = Util.selectRandomlyFromList(csp.getDomain(var).asList());
result.add(var, randomValue);
}
return(result);
}
/** Returns the values of Dom(var) in a special order. The least constraining value comes first. */
public ICollection <VAL> apply(CSP <VAR, VAL> csp, Assignment <VAR, VAL> assignment, VAR var)
{
ICollection <Pair <VAL, int> > pairs = CollectionFactory.CreateQueue <Pair <VAL, int> >();
foreach (VAL value in csp.getDomain(var))
{
int num = countLostValues(csp, assignment, var, value);
pairs.Add(new Pair <VAL, int>(value, num));
}
pairs.Sort(new PairComparer <VAL>());
ICollection <VAL> obj = CollectionFactory.CreateQueue <VAL>();
foreach (Pair <VAL, int> val in pairs)
{
obj.Add(val.GetFirst());
}
return(obj);
}
/** Returns variables from <code>vars</code> which are the best with respect to MRV. */
public ICollection <VAR> apply(CSP <VAR, VAL> csp, ICollection <VAR> vars)
{
ICollection <VAR> result = CollectionFactory.CreateQueue <VAR>();
int mrv = int.MaxValue;
foreach (VAR var in vars)
{
int rv = csp.getDomain(var).size();
if (rv <= mrv)
{
if (rv < mrv)
{
result.Clear();
mrv = rv;
}
result.Add(var);
}
}
return(result);
}
private VAL getMinConflictValueFor(VAR var, Assignment <VAR, VAL> assignment, CSP <VAR, VAL> csp)
{
ICollection <IConstraint <VAR, VAL> > constraints = csp.getConstraints(var);
Assignment <VAR, VAL> testAssignment = assignment.Clone();
int minConflict = int.MaxValue;
ICollection <VAL> resultCandidates = CollectionFactory.CreateQueue <VAL>();
foreach (VAL value in csp.getDomain(var))
{
testAssignment.add(var, value);
int currConflict = countConflicts(testAssignment, constraints);
if (currConflict <= minConflict)
{
if (currConflict < minConflict)
{
resultCandidates.Clear();
minConflict = currConflict;
}
resultCandidates.Add(value);
}
}
return((!resultCandidates.IsEmpty()) ? Util.selectRandomlyFromList <VAL>(resultCandidates) : default(VAL));
}
