/**
* 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;
}
/**
* 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 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);
}
/**
* 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());
}
/**
* 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;
}
/**
* 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);
}
/**
* 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);
}
/**
* 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, 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;
}
/**
* 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());
}
// //////////////////////////////////////////////////////////////
// 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;
}
