public DfaStateSet IntersectWith(DfaStateSet other)
{
var intersect = new HashSet <DfaState>(this.set);
intersect.IntersectWith(other.set);
return(new DfaStateSet(intersect));
}
public DfaStateSet ExceptWith(DfaStateSet other)
{
var except = new HashSet <DfaState>(this.set);
except.ExceptWith(other.set);
return(new DfaStateSet(except));
}
private void MergeStates()
{
//
// https://en.wikipedia.org/wiki/DFA_minimization
// Hopcroft's algorithm
//
var finals = new DfaStateSet(FinalStates);
var nons = new DfaStateSet(NonFinalStates);
var partitions = new List <DfaStateSet> {
finals, nons
};
var working = new List <DfaStateSet> {
finals
};
var terminals = new HashSet <Atom>(AllStates.SelectMany(state => state.Transitions).Select(transition => transition.Terminal));
while (working.Count > 0)
{
var a = working[0];
working.RemoveAt(0);
foreach (var terminal in terminals)
{
var x = new DfaStateSet();
foreach (var state in AllStates)
{
foreach (var transition in state.Transitions)
{
if (transition.Terminal.Set.Overlaps(terminal.Set))
{
if (a.Contains(transition.Target))
{
x.Add(state);
break;
}
}
}
}
var i = 0;
while (i < partitions.Count)
{
var y = partitions[i];
var x_intersect_y = x.IntersectWith(y);
var y_without_x = y.ExceptWith(x);
if (x_intersect_y.IsEmpty || y_without_x.IsEmpty)
{
i += 1;
continue;
}
partitions[i] = x_intersect_y;
i += 1;
partitions.Insert(i, y_without_x);
i += 1;
var j = 0;
while (j < working.Count)
{
if (working[j] == y)
{
working.RemoveAt(j);
working.Add(x_intersect_y);
working.Add(y_without_x);
break;
}
j += 1;
}
if (j == working.Count)
{
// ReSharper disable once ConvertIfStatementToConditionalTernaryExpression
if (x_intersect_y.Count <= y_without_x.Count)
{
working.Add(x_intersect_y);
}
else
{
working.Add(y_without_x);
}
}
}
}
}
foreach (var partition in partitions)
{
if (partition.Count > 1)
{
var dfaStates = partition.ToList();
var premium = dfaStates.First();
var remove = dfaStates.Skip(1).ToList();
foreach (var state in AllStates)
{
foreach (var transition in state.Transitions)
{
if (remove.Contains(transition.Target))
{
transition.Retarget(premium);
}
}
}
}
}
SetDfa(Dfa);
}
