// postfixExp to NFA
public NFA TransiteToFNA(String postfixExp)
{
if (postfixExp.Length == 0)
{
return(new EpsilonNFA());
}
Stack <NFA> stack = new Stack <NFA>();
foreach (Char token in postfixExp)
{
if (token == '*')
{
stack.Push(Closure(stack.Pop()));
}
else if (token == '|')
{
NFA right = stack.Pop();
NFA left = stack.Pop();
stack.Push(Union(left, right));
}
else if (token == '.')
{
NFA right = stack.Pop();
NFA left = stack.Pop();
stack.Push(Concat(left, right));
}
else
{
stack.Push(new SymbolNFA(token));
}
}
return(stack.Pop());
}
// concat two NFAs
public NFA Concat(NFA first, NFA second)
{
first.end.addEpsilonTransition(second.end);
first.end.setIsEnd(false);
NFA concated = new NFA(first.start, second.end);
return(concated);
}
// closure nfa
public NFA Closure(NFA nfa)
{
State start = new State(false);
State end = new State(true);
start.addEpsilonTransition(end);
start.addEpsilonTransition(nfa.start);
nfa.end.addEpsilonTransition(end);
nfa.end.addEpsilonTransition(nfa.start);
nfa.end.setIsEnd(false);
NFA closured = new NFA(start, end);
return(closured);
}
// union two NFAs
public NFA Union(NFA first, NFA second)
{
State start = new State(false);
State end = new State(true);
start.addEpsilonTransition(first.start);
end.addEpsilonTransition(second.start);
first.end.addEpsilonTransition(end);
first.end.setIsEnd(false);
second.end.addEpsilonTransition(end);
second.end.setIsEnd(false);
NFA unioned = new NFA(start, end);
return(unioned);
}
public Regex(String regularExpression)
{
Engine engine = new Engine();
this.nfa = engine.TransiteToFNA(regularExpression);
}