/// <summary>
/// Prunes all the unreachable states from this automaton
/// </summary>
public void Prune()
{
DFAInverse inverse = new DFAInverse(this);
List <DFAState> finals = inverse.CloseByAntecedents(inverse.Finals);
// no changes
if (finals.Count == states.Count)
{
return;
}
// Prune the transitions
for (int i = 0; i != finals.Count; i++)
{
DFAState state = finals[i];
List <CharSpan> transitions = new List <CharSpan>(state.Transitions);
foreach (CharSpan key in transitions)
{
DFAState child = state.GetChildBy(key);
if (!finals.Contains(child))
{
// the child should be dropped
state.RemoveTransition(key);
}
}
}
// prune
DFAState first = states[0];
finals.Remove(states[0]);
states.Clear();
states.Add(first);
states.AddRange(finals);
}
/// <summary>
/// Extracts the sub-DFA that leads to any of the specified states
/// </summary>
/// <param name="targets">States in this DFA</param>
/// <returns>The sub-DFA for the specified states</returns>
public DFA ExtractSubTo(IEnumerable <DFAState> targets)
{
if (targets == null)
{
throw new System.ArgumentException("The specified collection must not be null");
}
// build a list of all the required states
DFAInverse inverse = new DFAInverse(this);
List <DFAState> originals = inverse.CloseByAntecedents(targets);
// setup the list
int index = originals.IndexOf(states[0]);
if (index == -1)
{
throw new System.ArgumentException("The specified states are not reachable from the starting state");
}
originals[index] = originals[0];
originals[0] = states[0];
// copies the states
List <DFAState> copy = new List <DFAState>();
for (int i = 0; i != originals.Count; i++)
{
copy.Add(new DFAState(i));
}
for (int i = 0; i != originals.Count; i++)
{
DFAState original = originals[i];
DFAState clone = copy[i];
clone.AddItems(original.Items);
foreach (CharSpan key in original.Transitions)
{
index = originals.IndexOf(original.GetChildBy(key));
if (index != -1)
{
clone.AddTransition(key, copy[index]);
}
}
}
return(new DFA(copy));
}
/// <summary>
/// Determines whether two states should be in the same group
/// </summary>
/// <param name="s1">A state</param>
/// <param name="s2">Another state</param>
/// <param name="old">The old partition</param>
/// <returns></returns>
private static bool AddState_SameGroup(DFAState s1, DFAState s2, DFAPartition old)
{
if (s1.Transitions.Count != s2.Transitions.Count)
{
return(false);
}
// For each transition from state 1
foreach (CharSpan key in s1.Transitions)
{
// If state 2 does not have a transition with the same value : not same group
if (!s2.HasTransition(key))
{
return(false);
}
// Here State1 and State2 have both a transition of the same value
// If the target of these transitions are in the same group in the old partition : same transition
if (old.AddState_GetGroupOf(s1.GetChildBy(key)) != old.AddState_GetGroupOf(s2.GetChildBy(key)))
{
return(false);
}
}
return(true);
}
