private void UnitPropagation(TrailNode node, out Conflict conflict)
{
conflict = null;
foreach (var clause in ClauseReferences[node.Literal.index])
{
if (TryPropagate(node, clause, out bool error) is Literal empty)
{
AssignLiteral(empty);
var newNode = new TrailNode(level, empty, clause);
trail.Add(newNode);
UnitPropagation(newNode, out conflict);
if (conflict != null)
{
return;
}
}
if (error)
{
var learnedClause = trail.GetUIP(clause, out int targetLevel);
conflict = new Conflict(targetLevel, learnedClause);
return;
}
}
}
private TrailNode Backtrack()
{
var conflict = latestConflict;
latestConflict = null;
AddClause(conflict.Clause);
RevertToLevel(conflict.Level);
ApplyVSIDS(conflict.Clause);
var empty = FindEmpty(conflict.Clause);
if (debug)
{
Console.WriteLine($"Revert to level {level} | Learned: {conflict.Clause} | Empty: {string.Join(" ", empty)}");
StateDebug();
}
if (empty.Count == 1)
{
AssignLiteral(empty[0]);
var node = new TrailNode(level, empty[0], conflict.Clause);
trail.Add(node);
return(node);
}
else
{
return(Decision());
}
}
private TrailNode Decision(Literal?force = null)
{
level++;
Literal literal = force ?? SelectLiteral();
AssignLiteral(literal);
var node = new TrailNode(level, literal);
trail.Add(node);
return(node);
}
private Literal?TryPropagate(TrailNode node, Clause clause, out bool conflict)
{
int assignedValues = 0;
int falseValues = 0;
Literal empty = default;
conflict = false;
foreach (var lit in clause)
{
if (literals[lit.index].HasValue)
{
if (literals[lit.index].Value.value != lit.value)
{
falseValues++;
}
assignedValues++;
}
else
{
empty = lit;
}
}
if (assignedValues != falseValues)
{
return(null);
}
if (assignedValues == clause.Count - 1)
{
return(empty);
}
if (falseValues == clause.Count)
{
conflict = true;
return(null);
}
return(null);
}
private void InitialUnitPropagation(out Conflict conflict)
{
conflict = null;
foreach (var clause in Clauses)
{
if (clause.Count == 1)
{
Literal literal = clause[0];
if (!literals[literal.index].HasValue)
{
AssignLiteral(literal);
var node = new TrailNode(level, literal, clause);
trail.Add(node);
UnitPropagation(node, out conflict);
if (conflict != null)
{
return;
}
}
}
}
}
public override SolverResult Run()
{
if (Running)
{
throw new InvalidOperationException("Solver is already running");
}
Running = true;
totalwatch = Stopwatch.StartNew();
InitialUnitPropagation(out Conflict conflict);
if (conflict != null)
{
Running = false;
return(SolverResult.Fail(0));
}
if (AllAssigned)
{
Running = false;
return(SolverResult.Success(0, literals));
}
if (debug)
{
Console.WriteLine();
}
while (true)
{
if (debug && latestConflict != null)
{
Console.WriteLine("- Conflict");
Console.WriteLine(trail.DebugMessage);
}
iterations++;
TrailNode node = Travel();
UnitPropagation(node, out conflict);
if (debug)
{
StateDebug();
}
if (conflict == null && AllAssigned)
{
Running = false;
return(SolverResult.Success(iterations, literals));
}
if (conflict != null && level == 0)
{
Running = false;
return(SolverResult.Fail(iterations));
}
if (conflict != null)
{
latestConflict = conflict;
}
if (timeout != 0 && totalwatch.ElapsedMilliseconds > timeout)
{
Running = false;
return(SolverResult.Timeout(iterations, (int)totalwatch.ElapsedMilliseconds));
}
}
}