// checks if the given text matches the regexp
// if it does return true (its possible to reach state M in the NFA)
// Logic:
// 1) create a list of states that are reachable from 0 : ps
// 2) create a list of states that are reachable after processing text.CharAt(i) : matches
// 3) update ps with list of states that are reachable from matches
// 4) if ever PS has a state that is the last state, then the given text matches the regexp
public bool Matches(string text)
{
List <int> ps = new List <int>();
DirectedDFS dfs = new DirectedDFS(G, 0);
// states reachable from start by e-transitions
for (int i = 0; i < G.Vertices(); i++)
{
if (dfs.marked(i))
{
ps.Add(i);
}
}
for (int i = 0; i < text.Length; i++)
{
List <int> match = new List <int>();
// states reachable after scanning past txt.charAt(i)
foreach (int v in ps)
{
if (v == M)
{
return(true);
}
if (re[v] == text[i] || re[v] == '.') // since '.' indicates any character, it is considered a match
{
match.Add(v + 1);
}
}
dfs = new DirectedDFS(G, match);
ps = new List <int>();
for (int v = 0; v < G.Vertices(); v++)
{
if (dfs.marked(v))
{
ps.Add(v);
}
}
}
foreach (int v in ps)
{
if (v == M)
{
return(true);
}
}
return(false);
}
