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);
}
}
// //////////////////////////////////////////////////////////////
// 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 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);
}
/**
* Template method, which can be configured by overriding the three
* primitive operations below.
*/
private Assignment recursiveBackTrackingSearch(CSP csp,
Assignment assignment)
{
Assignment result = null;
if (assignment.isComplete(csp.getVariables()))
{
result = assignment;
}
else
{
Variable var = selectUnassignedVariable(assignment, csp);
foreach (Object value in orderDomainValues(var, assignment, csp))
{
assignment.setAssignment(var, value);
fireStateChanged(assignment, csp);
if (assignment.isConsistent(csp.getConstraints(var)))
{
DomainRestoreInfo info = inference(var, assignment, csp);
if (!info.isEmpty())
fireStateChanged(csp);
if (!info.isEmptyDomainFound())
{
result = recursiveBackTrackingSearch(csp, assignment);
if (result != null)
break;
}
info.restoreDomains(csp);
}
assignment.removeAssignment(var);
}
}
return result;
}
private List<Variable> getConflictedVariables(Assignment assignment, CSP csp) {
List<Variable> result = new List<Variable>();
foreach (Constraint constraint in csp.getConstraints())
{
if (!constraint.isSatisfiedWith(assignment))
foreach (Variable var in constraint.getScope())
if (!result.contains(var))
result.Add(var);
}
return result;
}
private List <Variable> getConflictedVariables(Assignment assignment, CSP csp)
{
List <Variable> result = new List <Variable>();
foreach (Constraint constraint in csp.getConstraints())
{
if (!constraint.isSatisfiedWith(assignment))
{
foreach (Variable var in constraint.getScope())
{
if (!result.contains(var))
{
result.Add(var);
}
}
}
}
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);
}
/**
* Template method, which can be configured by overriding the three
* primitive operations below.
*/
private Assignment recursiveBackTrackingSearch(CSP csp,
Assignment assignment)
{
Assignment result = null;
if (assignment.isComplete(csp.getVariables()))
{
result = assignment;
}
else
{
Variable var = selectUnassignedVariable(assignment, csp);
foreach (Object value in orderDomainValues(var, assignment, csp))
{
assignment.setAssignment(var, value);
fireStateChanged(assignment, csp);
if (assignment.isConsistent(csp.getConstraints(var)))
{
DomainRestoreInfo info = inference(var, assignment, csp);
if (!info.isEmpty())
{
fireStateChanged(csp);
}
if (!info.isEmptyDomainFound())
{
result = recursiveBackTrackingSearch(csp, assignment);
if (result != null)
{
break;
}
}
info.restoreDomains(csp);
}
assignment.removeAssignment(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 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 is consistent as well as complete with
* respect to the given CSP.
*/
public bool isSolution(CSP csp)
{
return(isConsistent(csp.getConstraints()) &&
isComplete(csp.getVariables()));
}
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);
}
}
}
}
}
/**
* Returns true if this assignment is consistent as well as complete with
* respect to the given CSP.
*/
public bool isSolution(CSP csp)
{
return isConsistent(csp.getConstraints())
&& isComplete(csp.getVariables());
}
// //////////////////////////////////////////////////////////////
// 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;
}
/** : 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;
}
