// B->C*{starNFA}|C+{plusNFA}|C
private bool EvalB()
{
int saved_index = current_index_;
if (!EvalC())
{
current_index_ = saved_index;
return(false);
}
bool success = false;
saved_index = current_index_;
do
{
if (regex_.Length <= current_index_)
{
break;
}
if (regex_[current_index_] != '*' && regex_[current_index_] != '+')
{
break;
}
if (nfa_stack_.Count < 1)
{
break;
}
NFA op = nfa_stack_.Pop();
NFA result = null;
if (regex_[current_index_] == '*')
{
result = NFA.StarNFA(op);
}
else
{
result = NFA.PlusNFA(op);
}
if (result == null)
{
return(false);
}
nfa_stack_.Push(result);
current_index_++;
success = true;
} while (false);
if (!success)
{
current_index_ = saved_index;
}
return(true);
}
// S'->|A{unionNFA}S'|epsilon
private bool EvalSp()
{
bool success = false;
int saved_index = current_index_;
// S'->|A{unionNFA}S'
do
{
if (regex_.Length <= current_index_)
{
break;
}
if (regex_[current_index_] != '|')
{
break;
}
// S'->|A{unionNFA}S'
current_index_++;
if (!EvalA())
{
break;
}
if (nfa_stack_.Count < 2)
{
break;
}
NFA op2 = nfa_stack_.Pop();
NFA op1 = nfa_stack_.Pop();
NFA result = NFA.UnionNFA(op1, op2);
if (result == null)
{
return(false);
}
nfa_stack_.Push(result);
if (EvalSp() == false)
{
break;
}
success = true;
} while (false);
// not S'->|A{unionNFA}S'
// Use S'->epsilon
if (!success)
{
current_index_ = saved_index;
success = true;
}
return(success);
}
// C->(S)|others{createInput}
private bool EvalC()
{
int saved_index = current_index_;
if (regex_.Length <= current_index_)
{
return(false);
}
// C->(S)
if (regex_[current_index_++] == '(' &&
EvalS() &&
current_index_ < regex_.Length &&
regex_[current_index_++] == ')')
{
return(true);
}
// C->others{createInput}
char[] SPECIAL_MARK = { '(', ')', '*', '|', '\\', '+' };
current_index_ = saved_index;
if (regex_[current_index_] == '\\')
{
if (regex_.Length <= current_index_ + 1)
{
return(false);
}
if (!SPECIAL_MARK.Contains(regex_[current_index_ + 1]))
{
return(false);
}
current_index_++;
}
else if (SPECIAL_MARK.Contains(regex_[current_index_]))
{
return(false);
}
NFA result = NFA.CreateFromInput(regex_[current_index_]);
if (result == null)
{
current_index_ = saved_index;
return(false);
}
nfa_stack_.Push(result);
current_index_++;
return(true);
}
public static NFA CreateFromInput(char input)
{
AutomataStatus start = new AutomataStatus();
AutomataStatus end = new AutomataStatus();
start.AddTransition(input, end);
NFA nfa = new NFA();
nfa.startStatus_ = start;
nfa.endStatus_ = end;
return(nfa);
}
public static NFA PlusNFA(NFA op)
{
AutomataStatus start = new AutomataStatus();
AutomataStatus end = new AutomataStatus();
start.AddTransition((char)0, op.startStatus_);
op.endStatus_.AddTransition((char)0, end);
op.endStatus_.AddTransition((char)0, op.startStatus_);
NFA nfa = new NFA();
nfa.startStatus_ = start;
nfa.endStatus_ = end;
return(nfa);
}
// A'->B{concatNFA}A' | epsilon
private bool EvalAp()
{
bool success = false;
int saved_index = current_index_;
// A'->B{concatNFA}A'
do
{
if (!EvalB())
{
break;
}
if (nfa_stack_.Count < 2)
{
break;
}
NFA op2 = nfa_stack_.Pop();
NFA op1 = nfa_stack_.Pop();
NFA result = NFA.ConcatNFA(op1, op2);
if (result == null)
{
return(false);
}
nfa_stack_.Push(result);
if (!EvalAp())
{
break;
}
success = true;
} while (false);
// not A'->B{concatNFA}A'
// Use A'->epsilon
if (!success)
{
current_index_ = saved_index;
success = true;
}
return(success);
}
static void Main(string[] args)
{
NFATranslator t = new NFATranslator("ab*");
NFA nfa = t.GetNFA();
bool ret = nfa.Match("a");
}
