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);
}
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);
}
}
/** : the degree heuristic. */
private List <Variable> applyDegreeHeuristic(List <Variable> vars,
Assignment assignment, CSP csp)
{
List <Variable> result = new List <Variable>();
int maxDegree = int.MIN_VALUE;
foreach (Variable var in vars)
{
int degree = 0;
foreach (Constraint constraint in csp.getConstraints(var))
{
Variable neighbor = csp.getNeighbor(var, constraint);
if (!assignment.hasAssignmentFor(neighbor) &&
csp.getDomain(neighbor).Count > 1)
{
++degree;
}
}
if (degree >= maxDegree)
{
if (degree > maxDegree)
{
result.clear();
maxDegree = degree;
}
result.Add(var);
}
}
return(result);
}
// //////////////////////////////////////////////////////////////
// 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);
}
/** : 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);
}
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);
}
private Assignment generateRandomAssignment(CSP csp) {
Assignment assignment = new Assignment();
foreach (Variable var in csp.getVariables())
{
Object randomValue = Util.selectRandomlyFromList(csp.getDomain(var)
.asList());
assignment.setAssignment(var, randomValue);
}
return assignment;
}
/**
* 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 Assignment generateRandomAssignment(CSP csp)
{
Assignment assignment = new Assignment();
foreach (Variable var in csp.getVariables())
{
Object randomValue = Util.selectRandomlyFromList(csp.getDomain(var)
.asList());
assignment.setAssignment(var, randomValue);
}
return(assignment);
}
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);
}
/**
* 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();
}
/**
* 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());
}
// //////////////////////////////////////////////////////////////
// heuristics for selecting the next unassigned variable and domain ordering
/** : the minimum-remaining-values heuristic. */
private List <Variable> applyMRVHeuristic(CSP csp, Assignment assignment)
{
List <Variable> result = new List <Variable>();
int mrv = int.MAX_VALUE;
foreach (Variable var in csp.getVariables())
{
if (!assignment.hasAssignmentFor(var))
{
int num = csp.getDomain(var).Count;
if (num <= mrv)
{
if (num < mrv)
{
result.clear();
mrv = num;
}
result.Add(var);
}
}
}
return(result);
}
private void reduceDomains(FIFOQueue <Variable> queue, CSP csp,
DomainRestoreInfo info)
{
while (!queue.isEmpty())
{
Variable var = queue.pop();
foreach (Constraint constraint in csp.getConstraints(var))
{
if (constraint.getScope().Count == 2)
{
Variable neighbor = csp.getNeighbor(var, constraint);
if (revise(neighbor, var, constraint, csp, info))
{
if (csp.getDomain(neighbor).isEmpty())
{
info.setEmptyDomainFound(true);
return;
}
queue.push(neighbor);
}
}
}
}
}
private void reduceDomains(FIFOQueue<Variable> queue, CSP csp,
DomainRestoreInfo info)
{
while (!queue.isEmpty())
{
Variable var = queue.pop();
foreach (Constraint constraint in csp.getConstraints(var))
{
if (constraint.getScope().Count == 2)
{
Variable neighbor = csp.getNeighbor(var, constraint);
if (revise(neighbor, var, constraint, csp, info))
{
if (csp.getDomain(neighbor).isEmpty())
{
info.setEmptyDomainFound(true);
return;
}
queue.push(neighbor);
}
}
}
}
}
/** : 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;
}
/** : the degree heuristic. */
private List<Variable> applyDegreeHeuristic(List<Variable> vars,
Assignment assignment, CSP csp)
{
List<Variable> result = new List<Variable>();
int maxDegree = int.MIN_VALUE;
foreach (Variable var in vars)
{
int degree = 0;
foreach (Constraint constraint in csp.getConstraints(var))
{
Variable neighbor = csp.getNeighbor(var, constraint);
if (!assignment.hasAssignmentFor(neighbor)
&& csp.getDomain(neighbor).Count > 1)
++degree;
}
if (degree >= maxDegree)
{
if (degree > maxDegree)
{
result.clear();
maxDegree = degree;
}
result.Add(var);
}
}
return result;
}
// //////////////////////////////////////////////////////////////
// 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;
}
/**
* 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;
}
/**
* 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);
}
/**
* 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));
}
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;
}
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;
}
// //////////////////////////////////////////////////////////////
// heuristics for selecting the next unassigned variable and domain ordering
/** : the minimum-remaining-values heuristic. */
private List<Variable> applyMRVHeuristic(CSP csp, Assignment assignment)
{
List<Variable> result = new List<Variable>();
int mrv = int.MAX_VALUE;
foreach (Variable var in csp.getVariables())
{
if (!assignment.hasAssignmentFor(var))
{
int num = csp.getDomain(var).Count;
if (num <= mrv)
{
if (num < mrv)
{
result.clear();
mrv = num;
}
result.Add(var);
}
}
}
return result;
}
