/**
* Stores the specified domain for the specified variable if a domain has
* not yet been stored for the variable.
*/
public void storeDomainFor(Variable var, Domain domain)
{
if (!affectedVariables.contains(var))
{
savedDomains.Add(new Pair<Variable, Domain>(var, domain));
affectedVariables.Add(var);
}
}
public NotEqualConstraint(Variable var1, Variable var2)
{
this.var1 = var1;
this.var2 = var2;
scope = new List<Variable>(2);
scope.Add(var1);
scope.Add(var2);
}
public void removeAssignment(Variable var)
{
if (hasAssignmentFor(var))
{
variables.remove(var);
variableToValue.remove(var);
}
}
/**
* Replaces the domain of the specified variable by new domain,
* which contains all values of the old domain except the specified
* value.
*/
public void removeValueFromDomain(Variable var, Object value)
{
Domain currDomain = getDomain(var);
List<Object> values = new List<Object>(currDomain.Count);
foreach (Object v in currDomain)
if (!v.Equals(value))
values.Add(v);
setDomain(var, new Domain(values));
}
/**
* Reduces the domain of the specified variable to the specified
* value and reestablishes arc-consistency. It is assumed that the
* provided CSP is arc-consistent before the call.
* @return An object which indicates success/failure and contains
* data to undo the operation.
*/
public DomainRestoreInfo reduceDomains(Variable var, Object value, CSP csp)
{
DomainRestoreInfo result = new DomainRestoreInfo();
Domain domain = csp.getDomain(var);
if (domain.contains(value))
{
if (domain.Count > 1)
{
FIFOQueue<Variable> queue = new FIFOQueue<Variable>();
queue.Add(var);
result.storeDomainFor(var, domain);
csp.setDomain(var, new Domain(new Object[] { value }));
reduceDomains(queue, csp, result);
}
}
else
{
result.setEmptyDomainFound(true);
}
return result.compactify();
}
private bool revise(Variable xi, Variable xj, Constraint constraint,
CSP csp, DomainRestoreInfo info)
{
bool revised = false;
Assignment assignment = new Assignment();
foreach (Object iValue in csp.getDomain(xi))
{
assignment.setAssignment(xi, iValue);
bool consistentExtensionFound = false;
foreach (Object jValue in csp.getDomain(xj))
{
assignment.setAssignment(xj, jValue);
if (constraint.isSatisfiedWith(assignment))
{
consistentExtensionFound = true;
break;
}
}
if (!consistentExtensionFound)
{
info.storeDomainFor(xi, csp.getDomain(xi));
csp.removeValueFromDomain(xi, iValue);
revised = true;
}
}
return revised;
}
/** : the least constraining value heuristic. */
private List<Object> applyLeastConstrainingValueHeuristic(Variable var,
CSP csp)
{
List<Pair<Object, int>> pairs = new List<Pair<Object, int>>();
foreach (Object value in csp.getDomain(var))
{
int num = countLostValues(var, value, csp);
pairs.Add(new Pair<Object, int>(value, num));
}
// TODO
//Collections.sort(pairs, new Comparator<Pair<Object, int>>() {
// public int compare(Pair<Object, int> o1,
// Pair<Object, int> o2) {
// return o1.getSecond() < o2.getSecond() ? -1
// : o1.getSecond() > o2.getSecond() ? 1 : 0;
// }
//});
List<Object> result = new List<Object>();
foreach (Pair<Object, int> pair in pairs)
result.Add(pair.getFirst());
return result;
}
public Domain getDomain(Variable var)
{
return domains.get(varIndexHash.get(var));
}
/**
* Returns for binary constraints the other variable from the scope.
*
* @return a variable or null for non-binary constraints.
*/
public Variable getNeighbor(Variable var, Constraint constraint)
{
List<Variable> scope = constraint.getScope();
if (scope.Count == 2)
{
if (var == scope.get(0))
return scope.get(1);
else if (var == scope.get(1))
return scope.get(0);
}
return null;
}
public bool hasAssignmentFor(Variable var)
{
return(variableToValue.get(var) != null);
}
public void setAssignment(Variable var, Object value)
{
if (!variableToValue.containsKey(var))
variables.Add(var);
variableToValue.put(var, value);
}
public Object getAssignment(Variable var)
{
return variableToValue.get(var);
}
/**
* Primitive operation, ordering the domain values of the specified
* variable.
*/
protected override Iterable? orderDomainValues(Variable var,
Assignment assignment, CSP csp)
{
if (!isLCVHeuristicEnabled)
{
return csp.getDomain(var);
}
else
{
return applyLeastConstrainingValueHeuristic(var, csp);
}
}
private bool revise(Variable var, Constraint constraint,
Assignment assignment, CSP csp, DomainRestoreInfo info)
{
bool revised = false;
foreach (Object value in csp.getDomain(var))
{
assignment.setAssignment(var, value);
if (!constraint.isSatisfiedWith(assignment))
{
info.storeDomainFor(var, csp.getDomain(var));
csp.removeValueFromDomain(var, value);
revised = true;
}
assignment.removeAssignment(var);
}
return revised;
}
// //////////////////////////////////////////////////////////////
// inference algorithms
/** : forward checking. */
private DomainRestoreInfo doForwardChecking(Variable var,
Assignment assignment, CSP csp)
{
DomainRestoreInfo result = new DomainRestoreInfo();
foreach (Constraint constraint in csp.getConstraints(var))
{
List<Variable> scope = constraint.getScope();
if (scope.Count == 2)
{
foreach (Variable neighbor in constraint.getScope())
{
if (!assignment.hasAssignmentFor(neighbor))
{
if (revise(neighbor, constraint, assignment, csp,
result))
{
if (csp.getDomain(neighbor).isEmpty())
{
result.setEmptyDomainFound(true);
return result;
}
}
}
}
}
}
return result;
}
private int countLostValues(Variable var, Object value, CSP csp)
{
int result = 0;
Assignment assignment = new Assignment();
assignment.setAssignment(var, value);
foreach (Constraint constraint in csp.getConstraints(var))
{
Variable neighbor = csp.getNeighbor(var, constraint);
foreach (Object nValue in csp.getDomain(neighbor))
{
assignment.setAssignment(neighbor, nValue);
if (!constraint.isSatisfiedWith(assignment))
{
++result;
}
}
}
return result;
}
public Object getAssignment(Variable var)
{
return(variableToValue.get(var));
}
public bool hasAssignmentFor(Variable var)
{
return variableToValue.get(var) != null;
}
private Object getMinConflictValueFor(Variable var, Assignment assignment,
CSP csp) {
List<Constraint> constraints = csp.getConstraints(var);
Assignment duplicate = assignment.copy();
int minConflict = int.MAX_VALUE;
List<Object> resultCandidates = new List<Object>();
foreach (Object value in csp.getDomain(var))
{
duplicate.setAssignment(var, value);
int currConflict = countConflicts(duplicate, constraints);
if (currConflict <= minConflict) {
if (currConflict < minConflict) {
resultCandidates.clear();
minConflict = currConflict;
}
resultCandidates.Add(value);
}
}
if (!resultCandidates.isEmpty())
return Util.selectRandomlyFromList(resultCandidates);
else
return null;
}
/**
* Returns true if this assignment assigns values to every variable of
* <code>vars</code>.
*/
public bool isComplete(Variable[] vars)
{
foreach (Variable var in vars)
{
if (!hasAssignmentFor(var))
return false;
}
return true;
}
public int indexOf(Variable var)
{
return varIndexHash.get(var);
}
/**
* Primitive operation, ordering the domain values of the specified
* variable. This default implementation just takes the default order
* provided by the CSP.
*/
protected Iterable? orderDomainValues(Variable var,
Assignment assignment, CSP csp)
{
return csp.getDomain(var);
}
public void setDomain(Variable var, Domain domain)
{
domains.set(indexOf(var), domain);
}
/**
* Primitive operation, which tries to prune out values from the CSP which
* are not possible anymore when extending the given assignment to a
* solution. This default implementation just leaves the original CSP as it
* is.
*
* @return An object which provides informations about (1) whether changes
* have been performed, (2) possibly inferred empty domains , and
* (3) how to restore the domains.
*/
protected DomainRestoreInfo inference(Variable var, Assignment assignment,
CSP csp)
{
return new DomainRestoreInfo().compactify();
}
/**
* Returns all constraints in which the specified variable participates.
*/
public List<Constraint> getConstraints(Variable var)
{
return cnet.get(var);
}
/**
* Primitive operation, which tries to prune out values from the CSP which
* are not possible anymore when extending the given assignment to a
* solution.
*
* @return An object which provides informations about (1) whether changes
* have been performed, (2) possibly inferred empty domains , and
* (3) how to restore the domains.
*/
protected override DomainRestoreInfo inference(Variable var, Assignment assignment,
CSP csp)
{
switch (inferenceStrategy)
{
case FORWARD_CHECKING:
return doForwardChecking(var, assignment, csp);
case AC3:
return new AC3Strategy().reduceDomains(var, assignment
.getAssignment(var), csp);
default:
return new DomainRestoreInfo().compactify();
}
}
