/// <summary>
/// 使用一个队列辅助进行幂集构造，求出 DFA 的转移函数
/// </summary>
/// <param name="nfaTransitionFunctions">NFA 的转移函数</param>
/// <param name="inputs">字母表</param>
/// <param name="initalTransitionFunction">初始转移函数</param>
/// <returns></returns>
private static HashSet <TransitionFunction> NfaToDfaTransitionFunctions(
HashSet <TransitionFunction> nfaTransitionFunctions,
SortedSet <char> inputs,
HashSet <TransitionFunction> initalTransitionFunction)
{
var dfaTransitionFunctionsQueue = new Queue <TransitionFunction>();
var dfaTransitionFunctions = new HashSet <TransitionFunction>();
foreach (var func in initalTransitionFunction)
{
dfaTransitionFunctionsQueue.Enqueue(func);
}
while (dfaTransitionFunctionsQueue.Count != 0)
{
var func = dfaTransitionFunctionsQueue.Dequeue();
dfaTransitionFunctions.Add(func);
foreach (var input in inputs)
{
if (func.Input != input)
{
continue;
}
var nextStates = func.NextStates;
foreach (var enumInput in inputs)
{
if (enumInput == '$')
{
continue;
}
var nextNext = TransitionFunction.GetNextStatesOf(
nfaTransitionFunctions,
enumInput,
nextStates
);
var newFunc = new TransitionFunction(
nextStates,
enumInput,
nextNext
);
if (TransitionFunction.HasOld(dfaTransitionFunctions, newFunc))
{
continue;
}
dfaTransitionFunctionsQueue.Enqueue(newFunc);
}
}
}
return(dfaTransitionFunctions);
}
/// <summary>
/// 将 eNfa 转换为 Nfa
/// </summary>
/// <param name="eNfa"></param>
/// <returns></returns>
private static HashSet <TransitionFunction> RemoveEpsilonTransitions(Automata eNfa)
{
var nfaTransitionFunctions = new HashSet <TransitionFunction>();
foreach (var state in eNfa.States)
{
var eclosure = eNfa.GetEpsilonClosureOf(state);
foreach (var eclosureState in eclosure)
{
var acceptableInputs = eNfa.GetAcceptableInputOf(eclosureState, true);
foreach (var input in acceptableInputs)
{
var func = new TransitionFunction(eclosure, input, eNfa.GetNextStatesOf(eclosure, input));
nfaTransitionFunctions.Add(func);
}
}
}
return(nfaTransitionFunctions);
}
/// <summary>
/// 将 NFA(可带空转) 转换为 DFA
/// </summary>
/// <param name="eNfa">NFA</param>
/// <returns></returns>
public static Automata EpsilonNfaToDFA(Automata eNfa)
{
// 首先将 eNFA 转换为 NFA
var nfaTransitionFunctions = RemoveEpsilonTransitions(eNfa);
Debug.WriteLine("New transition functions:");
Debug.WriteLine(string.Join("\n", nfaTransitionFunctions));
var dfa = new AutomataBuilder()
.SetInputSymbols(eNfa.InputSymbols.ToArray())
.Build();
// 获取初始转移函数
var initalTransitionFunction = TransitionFunction.GetInitalTransitionFunction(nfaTransitionFunctions, eNfa.InitialState);
if (0 == initalTransitionFunction.Count)
{
throw new Exception("Initial transition function not found!");
}
var dfaTransitionFunctions = NfaToDfaTransitionFunctions(nfaTransitionFunctions, dfa.InputSymbols, initalTransitionFunction);
var stateMap = TransitionFunction.MergeStates(dfaTransitionFunctions);
dfa.States = new SortedSet <State>();
foreach (var kv in stateMap)
{
dfa.States.Add(new State(kv.Value.Name, kv.Key));
}
SortedSet <State> finalStates = GetFinialStates(eNfa, dfa);
dfa.FinalStates = finalStates;
dfa.InitialState = stateMap[eNfa.InitialState.Name];
var mergedFunctions = TransitionFunction.MergeFunctions(dfaTransitionFunctions, stateMap);
dfa.TransitionFunctions = mergedFunctions;
Debug.WriteLine("DFA transition functions:");
Debug.WriteLine(string.Join("\n", dfaTransitionFunctions));
return(dfa);
}
/// <summary>
/// 判断转移函数是否重复
/// </summary>
/// <param name="dfaTransitionFunctions"></param>
/// <param name="newFunc"></param>
/// <returns></returns>
public static bool HasOld(HashSet <TransitionFunction> dfaTransitionFunctions, TransitionFunction newFunc)
{
foreach (var func in dfaTransitionFunctions)
{
if (func.Input == newFunc.Input && func.PresentStates.SetEquals(newFunc.PresentStates))
{
return(true);
}
}
return(false);
}
