/**
* 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;
}
/**
* Makes a CSP consisting of binary constraints arc-consistent.
* @return An object which indicates success/failure and contains
* data to undo the operation.
*/
public DomainRestoreInfo reduceDomains(CSP csp)
{
DomainRestoreInfo result = new DomainRestoreInfo();
FIFOQueue<Variable> queue = new FIFOQueue<Variable>();
foreach (Variable var in csp.getVariables())
queue.Add(var);
reduceDomains(queue, csp, result);
return result.compactify();
}
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 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;
}
/**
* Starts with a constraint propagation if AC-3 is enabled and then calls
* the super class implementation.
*/
public Assignment solve(CSP csp)
{
if (inferenceStrategy == Inference.AC3)
{
DomainRestoreInfo info = new AC3Strategy().reduceDomains(csp);
if (!info.isEmpty())
{
fireStateChanged(csp);
if (info.isEmptyDomainFound())
return null;
}
}
return super.solve(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, selecting a not yet assigned variable.
*/
protected override Variable selectUnassignedVariable(Assignment assignment, CSP csp)
{
switch (selectionStrategy)
{
case MRV:
return applyMRVHeuristic(csp, assignment).get(0);
case MRV_DEG:
List<Variable> vars = applyMRVHeuristic(csp, assignment);
return applyDegreeHeuristic(vars, assignment, csp).get(0);
default:
foreach (Variable var in csp.getVariables())
{
if (!(assignment.hasAssignmentFor(var)))
return var;
}
}
return null;
}
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);
}
/**
* 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();
}
public Assignment solve(CSP csp)
{
Assignment assignment = generateRandomAssignment(csp);
fireStateChanged(assignment, csp);
for (int i = 0; i < maxSteps; i++)
{
if (assignment.isSolution(csp))
{
return assignment;
}
else
{
List<Variable> vars = getConflictedVariables(assignment, csp);
Variable var = Util.selectRandomlyFromList(vars);
Object value = getMinConflictValueFor(var, assignment, csp);
assignment.setAssignment(var, value);
fireStateChanged(assignment, csp);
}
}
return null;
}
/**
* Primitive operation, selecting a not yet assigned variable.
*/
protected override Variable selectUnassignedVariable(Assignment assignment, CSP csp)
{
switch (selectionStrategy)
{
case MRV:
return(applyMRVHeuristic(csp, assignment).get(0));
case MRV_DEG:
List <Variable> vars = applyMRVHeuristic(csp, assignment);
return(applyDegreeHeuristic(vars, assignment, csp).get(0));
default:
foreach (Variable var in csp.getVariables())
{
if (!(assignment.hasAssignmentFor(var)))
{
return(var);
}
}
}
return(null);
}
public Assignment solve(CSP csp)
{
Assignment assignment = generateRandomAssignment(csp);
fireStateChanged(assignment, csp);
for (int i = 0; i < maxSteps; i++)
{
if (assignment.isSolution(csp))
{
return(assignment);
}
else
{
List <Variable> vars = getConflictedVariables(assignment, csp);
Variable var = Util.selectRandomlyFromList(vars);
Object value = getMinConflictValueFor(var, assignment, csp);
assignment.setAssignment(var, value);
fireStateChanged(assignment, csp);
}
}
return(null);
}
/**
* 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());
}
/**
* 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);
}
// //////////////////////////////////////////////////////////////
// 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);
}
}
}
}
}
public void restoreDomains(CSP csp)
{
foreach (Pair<Variable, Domain> pair in getSavedDomains())
csp.setDomain(pair.getFirst(), pair.getSecond());
}
public abstract Assignment solve(CSP csp);
protected void fireStateChanged(Assignment assignment, CSP csp)
{
foreach (CSPStateListener listener in listeners)
listener.stateChanged(assignment.copy(), csp.copyDomains());
}
protected void fireStateChanged(CSP csp)
{
foreach (CSPStateListener listener in listeners)
listener.stateChanged(csp.copyDomains());
}
/**
* 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());
}
/** : 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;
}
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;
}
/**
* 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);
}
/**
* 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()));
}
/**
* 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, selecting a not yet assigned variable. This default
* implementation just selects the first in the ordered list of variables
* provided by the CSP.
*/
protected Variable selectUnassignedVariable(Assignment assignment, CSP csp)
{
foreach (Variable var in csp.getVariables())
{
if (!(assignment.hasAssignmentFor(var)))
return var;
}
return null;
}
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;
}
public Assignment solve(CSP csp)
{
return recursiveBackTrackingSearch(csp, new Assignment());
}
/**
* 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();
}
/** : 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 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;
}
// //////////////////////////////////////////////////////////////
// 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;
}
/**
* Returns a copy which contains a copy of the domains list and is in all
* other aspects a flat copy of this.
*/
public CSP copyDomains()
{
CSP result = new CSP();
result.variables = variables;
result.domains = new List<Domain>(domains.Count);
result.domains.AddRange(domains);
result.constraints = constraints;
result.varIndexHash = varIndexHash;
result.cnet = cnet;
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, 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();
}
}
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);
}
}
}
}
}
/**
* 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());
}
/**
* 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);
}
}
public Assignment solve(CSP csp)
{
return(recursiveBackTrackingSearch(csp, new Assignment()));
}
public abstract Assignment solve(CSP csp);
