/// <summary>
/// Converts NFA to DFA using "Subset Construction"
/// </summary>
/// <param name="stateStartNfa">Starting state of NFA</param>
/// <param name="setMasterDfa">Contains set of all DFA states when this function returns</param>
/// <returns>Starting state of DFA</returns>
public static State ConvertToDfa(State stateStartNfa)
{
if (stateStartNfa == null)
{
throw new ArgumentNullException(nameof(stateStartNfa));
}
HashSet <string> setAllInput = new HashSet <string>();
HashSet <State> setAllState = new HashSet <State>();
GetAllStateAndInput(stateStartNfa, setAllState, setAllInput);
setAllInput.Remove(MetaSymbol.EPSILON);
NfaToDfaHelper helper = new NfaToDfaHelper();
HashSet <State> setMove = null;
HashSet <State> setE_closure = null;
// first, we get E_Closure of the start state of NFA ( just following the algorithm)
setE_closure = E_Closure(stateStartNfa);
State stateStartDfa = new State(); // create a new DFA state to represent the above E_Closure
// NOTE:
// we keep track of the NFA E_Closure and the DFA state that represent the E_Closure.
// we maintain a relationship between the NFA E_Closure and DFA state that represents the NFA E_Closure.
// all these are done in the NfaToDfaHelper class.
if (IsAcceptingGroup(setE_closure))
{
stateStartDfa.AcceptingState = true;
}
helper.AddDfaState(stateStartDfa, setE_closure);
// please see "subset construction" algorithm
// for clear understanding
State stateT = null;
HashSet <State> setT = null;
State stateU = null;
while ((stateT = helper.GetNextUnmarkedDfaState()) != null)
{
helper.Mark(stateT); // flag it to indicate that we have processed this state.
// the DFA state stateT represents a set of NFA E_Closure.
// so, we retrieve the E_Closure.
setT = helper.GetE_ClosureByDfaState(stateT);
foreach (string str in setAllInput)
{
setMove = Move(setT, str);
if (setMove.Count > 0)
{
setE_closure = E_Closure(setMove);
stateU = helper.FindDfaStateByE_Closure(setE_closure);
if (stateU == null) // so set setEnclosure must be a new one and we should crate a new DFA state
{
stateU = new State();
if (IsAcceptingGroup(setE_closure))
{
stateU.AcceptingState = true;
}
helper.AddDfaState(stateU, setE_closure); // add new state (as unmarked by default)
}
stateT.AddTransition(str, stateU);
}
} // end of foreach..loop
} // end of while..loop
return(stateStartDfa);
} // end of ConvertToDfa method
} // end of CreateNfa method
/// <summary>
/// Converts NFA to DFA using "Subset Construction"
/// </summary>
/// <param name="stateStartNfa">Starting state of NFA</param>
/// <param name="setMasterDfa">Contains set of all DFA states when this function returns</param>
/// <returns>Starting state of DFA</returns>
private State ConvertToDfa(State stateStartNfa)
{
//Subset Construction算法
Set setAllInput = new Set();
Set setAllState = new Set();
GetAllStateAndInput(stateStartNfa, setAllState, setAllInput);
setAllInput.RemoveElement(MetaSymbol.EPSILON);
NfaToDfaHelper helper = new NfaToDfaHelper();
Set setMove = null;
Set setEclosure = null;
// first, we get Eclosure of the start state of NFA ( just following the algoritham)
setEclosure = Eclosure(stateStartNfa);
State stateStartDfa = new State(); // create a new DFA state to represent the above Eclosure
// NOTE:
// we keep track of the NFA Eclosure and the DFA state that represent the Eclosure.
// we maintain a relationship between the NFA Eclosure and DFA state that represents the NFA Eclosure.
// all these are done in the NfaToDfaHelper class.
if (IsAcceptingGroup(setEclosure) == true)
{
stateStartDfa.AcceptingState = true;
}
helper.AddDfaState(stateStartDfa, setEclosure);
string sInputSymbol = String.Empty; // dummy
// please see "subset construction" algoritham
// for clear understanding
State stateT = null;
Set setT = null;
State stateU = null;
while ((stateT = helper.GetNextUnmarkedDfaState()) != null)
{
helper.Mark(stateT); // flag it to indicate that we have processed this state.
// the DFA state stateT represents a set of NFA Eclosure.
// so, we retrieve the Eclosure.
setT = helper.GetEclosureByDfaState(stateT);
foreach (object obj in setAllInput)
{
sInputSymbol = obj.ToString();
setMove = Move(setT, sInputSymbol);
if (setMove.IsEmpty() == false)
{
setEclosure = Eclosure(setMove);
stateU = helper.FindDfaStateByEclosure(setEclosure);
if (stateU == null) // so set setEclosure must be a new one and we should crate a new DFA state
{
stateU = new State();
if (IsAcceptingGroup(setEclosure) == true)
{
stateU.AcceptingState = true;
}
helper.AddDfaState(stateU, setEclosure); // add new state (as unmarked by default)
}
stateT.AddTransition(sInputSymbol, stateU);
}
} // end of foreach..loop
} // end of while..loop
return(stateStartDfa);
} // end of ConverToDfa method
