/// <summary>
/// Builds this inverse graph from the specified DFA
/// </summary>
/// <param name="dfa">A DFA</param>
public DFAInverse(DFA dfa)
{
reachable = new List <DFAState>();
inverses = new Dictionary <DFAState, List <DFAState> >();
finals = new List <DFAState>();
// transitive closure of the first state
reachable.Add(dfa.States[0]);
inverses.Add(dfa.States[0], new List <DFAState>());
for (int i = 0; i != reachable.Count; i++)
{
DFAState current = reachable[i];
foreach (DFAState next in current.Children)
{
if (!reachable.Contains(next))
{
reachable.Add(next);
inverses.Add(next, new List <DFAState>());
}
inverses[next].Add(current);
}
if (current.Items.Count != 0)
{
finals.Add(current);
}
}
}
/// <summary>
/// Creates a new state in this DFA
/// </summary>
/// <returns>The create state</returns>
public DFAState CreateState()
{
DFAState state = new DFAState(states.Count);
states.Add(state);
return(state);
}
/// <summary>
/// Closes the specified list of states through inverse transitions
/// </summary>
/// <param name="states">The list of states to close</param>
/// <returns>The closure</returns>
public List <DFAState> CloseByAntecedents(IEnumerable <DFAState> states)
{
List <DFAState> result = new List <DFAState>(states);
// transitive closure of the final states by their antecedents
// final states are all reachable
for (int i = 0; i != result.Count; i++)
{
DFAState state = result[i];
if (!inverses.ContainsKey(state))
{
continue;
}
foreach (DFAState antecedent in inverses[state])
{
if (!result.Contains(antecedent) && reachable.Contains(antecedent))
{
// this antecedent is reachable and not yet in the closure
// => add it to the closure
result.Add(antecedent);
}
}
}
return(result);
}
/// <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>
/// Initializes this dfa as equivalent to the given nfa
/// </summary>
/// <param name="nfa">A nfa</param>
public DFA(NFA nfa)
{
states = new List <DFAState>();
List <NFAStateSet> nfaStateSets = new List <NFAStateSet>();
// Create the first NFA set, add the entry and close it
NFAStateSet nfaInit = new NFAStateSet();
nfaStateSets.Add(nfaInit);
nfaInit.Add(nfa.StateEntry);
nfaInit.Close();
// Create the initial state for the DFA
DFAState dfaInit = new DFAState(0);
states.Add(dfaInit);
// For each set in the list of the NFA states
for (int i = 0; i != nfaStateSets.Count; i++)
{
// Normalize transitions
nfaStateSets[i].Normalize();
// Get the transitions for the set
Dictionary <CharSpan, NFAStateSet> transitions = nfaStateSets[i].GetTransitions();
// For each transition
foreach (CharSpan value in transitions.Keys)
{
// The child by the transition
NFAStateSet next = transitions[value];
// Search for the child in the existing sets
bool found = false;
for (int j = 0; j != nfaStateSets.Count; j++)
{
// An existing equivalent set is already present
if (nfaStateSets[j].Equals(next))
{
states[i].AddTransition(value, states[j]);
found = true;
break;
}
}
// The child is not already present
if (!found)
{
// Add to the sets list
nfaStateSets.Add(next);
// Create the corresponding DFA state
DFAState newState = new DFAState(states.Count);
states.Add(newState);
// Setup transition
states[i].AddTransition(value, newState);
}
}
// Add finals
states[i].AddItems(nfaStateSets[i].GetFinals());
}
}
private int GetDFAStates_GetGroupIndexOf(DFAState state)
{
for (int i = 0; i != groups.Count; i++)
{
if (groups[i].Contains(state))
{
return(i);
}
}
return(-1);
}
/// <summary>
/// Gets the group of the given state in this partition
/// </summary>
/// <param name="state">A state</param>
/// <returns>The corresponding group</returns>
private DFAStateGroup AddState_GetGroupOf(DFAState state)
{
foreach (DFAStateGroup group in groups)
{
if (group.Contains(state))
{
return(group);
}
}
return(null);
}
/// <summary>
/// Determines if the two states have the same marks
/// </summary>
/// <param name="left">The left state</param>
/// <param name="right">The right state</param>
/// <returns>True if the two states have the same marks</returns>
private bool DFAPartition_SameFinals(DFAState left, DFAState right)
{
if (left.Items.Count != right.Items.Count)
{
return(false);
}
foreach (FinalItem Final in left.Items)
{
if (!right.Items.Contains(Final))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Extracts the sub-DFA that leads to the specified state
/// </summary>
/// <param name="state">A state in this DFA</param>
/// <returns>The sub-DFA for the specified state</returns>
public DFA ExtractSubTo(DFAState state)
{
if (state == null)
{
throw new System.ArgumentException("The specified state must not be null");
}
if (!states.Contains(state))
{
throw new System.ArgumentException("The specified state is not in this DFA");
}
List <DFAState> targets = new List <DFAState>(1);
targets.Add(state);
return(ExtractSubTo(targets));
}
/// <summary>
/// Gets the new dfa states produced by this partition
/// </summary>
/// <returns>The dfa states produced by this partition</returns>
public List <DFAState> GetDFAStates()
{
// For each group in the partition
foreach (DFAStateGroup group in groups)
{
bool found = false;
foreach (DFAState state in group.States)
{
if (state.ID == 0)
{
groups.Remove(group);
groups.Insert(0, group);
found = true;
break;
}
}
if (found)
{
break;
}
}
List <DFAState> states = new List <DFAState>();
// For each group in the partition
// Create the coresponding state and add the finals
foreach (DFAStateGroup group in groups)
{
// Create a new state
DFAState newState = new DFAState(states.Count);
// Add the terminal from the group to the new state
newState.AddItems(group.Representative.Items);
states.Add(newState);
}
// Do linkage
for (int i = 0; i != groups.Count; i++)
{
foreach (CharSpan Key in groups[i].Representative.Transitions)
{
states[i].AddTransition(Key, states[GetDFAStates_GetGroupIndexOf(groups[i].Representative.GetChildBy(Key))]);
}
}
return(states);
}
/// <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>
/// Adds a state to this partition, coming from the given old partition
/// </summary>
/// <param name="state">The state to add</param>
/// <param name="old">The old partition</param>
public void AddState(DFAState state, DFAPartition old)
{
bool added = false;
// For each group in the resulting groups set
foreach (DFAStateGroup group in groups)
{
// If the current state can be in this resulting group according to the old partition :
if (AddState_SameGroup(group.Representative, state, old))
{
// Add the state to the group
group.AddState(state);
added = true;
}
}
// The state cannot be in any groups : create a new group
if (!added)
{
groups.Add(new DFAStateGroup(state));
}
}
/// <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);
}
/// <summary>
/// Adds a transition from this state
/// </summary>
/// <param name="value">The value on the transition</param>
/// <param name="next">The next state by the transition</param>
public void AddTransition(CharSpan value, DFAState next)
{
transitions.Add(value, next);
}
/// <summary>
/// Determines whether the given state is in this group
/// </summary>
/// <param name="state">A state</param>
/// <returns>True of the state is in this group</returns>
public bool Contains(DFAState state)
{
return(states.Contains(state));
}
/// <summary>
/// Adds a state to this group
/// </summary>
/// <param name="state">The state to add</param>
public void AddState(DFAState state)
{
states.Add(state);
}
/// <summary>
/// Initializes this group with a representative state
/// </summary>
/// <param name="init">The representative state</param>
public DFAStateGroup(DFAState init)
{
states = new List <DFAState>();
states.Add(init);
}