/**
* Returns true if the text is matched by the regular expression.
*
* @param txt the text
* @return {@code true} if the text is matched by the regular expression,
* {@code false} otherwise
*/
public boolean recognizes(String txt) {
DirectedDFS dfs = new DirectedDFS(graph, 0);
Bag<Integer> pc = new Bag<Integer>();
for (int v = 0; v < graph.V(); v++)
if (dfs.marked(v)) pc.add(v);
// Compute possible NFA states for txt[i+1]
for (int i = 0; i < txt.length(); i++) {
if (txt.charAt(i) == '*' || txt.charAt(i) == '|' || txt.charAt(i) == '(' || txt.charAt(i) == ')')
throw new IllegalArgumentException("text contains the metacharacter '" + txt.charAt(i) + "'");
Bag<Integer> match = new Bag<Integer>();
for (int v : pc) {
if (v == m) continue;
if ((regexp.charAt(v) == txt.charAt(i)) || regexp.charAt(v) == '.')
match.add(v+1);
}
dfs = new DirectedDFS(graph, match);
pc = new Bag<Integer>();
for (int v = 0; v < graph.V(); v++)
if (dfs.marked(v)) pc.add(v);
// optimization if no states reachable
if (pc.size() == 0) return false;
}
// check for accept state
for (int v : pc)
if (v == m) return true;
return false;
}
/**
* Unit tests the {@code DirectedDFS} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
// read in digraph from command-line argument
In in = new In(args[0]);
Digraph G = new Digraph(in);
// read in sources from command-line arguments
Bag<Integer> sources = new Bag<Integer>();
for (int i = 1; i < args.length; i++) {
int s = Integer.parseInt(args[i]);
sources.add(s);
}
// multiple-source reachability
DirectedDFS dfs = new DirectedDFS(G, sources);
// print out vertices reachable from sources
for (int v = 0; v < G.V(); v++) {
if (dfs.marked(v)) StdOut.print(v + " ");
}
StdOut.println();
}
private DirectedDFS[] tc; // tc[v] = reachable from v
/**
* Computes the transitive closure of the digraph {@code G}.
* @param G the digraph
*/
public TransitiveClosure(Digraph G) {
tc = new DirectedDFS[G.V()];
for (int v = 0; v < G.V(); v++)
tc[v] = new DirectedDFS(G, v);
}
