/**
* Initializes a digraph from a file using the specified delimiter.
* Each line in the file contains
* the name of a vertex, followed by a list of the names
* of the vertices adjacent to that vertex, separated by the delimiter.
* @param filename the name of the file
* @param delimiter the delimiter between fields
*/
public SymbolDigraph(String filename, String delimiter) {
st = new ST<String, Integer>();
// First pass builds the index by reading strings to associate
// distinct strings with an index
In in = new In(filename);
while (in.hasNextLine()) {
String[] a = in.readLine().split(delimiter);
for (int i = 0; i < a.length; i++) {
if (!st.contains(a[i]))
st.put(a[i], st.size());
}
}
// inverted index to get string keys in an aray
keys = new String[st.size()];
for (String name : st.keys()) {
keys[st.get(name)] = name;
}
// second pass builds the digraph by connecting first vertex on each
// line to all others
G = new Digraph(st.size());
in = new In(filename);
while (in.hasNextLine()) {
String[] a = in.readLine().split(delimiter);
int v = st.get(a[0]);
for (int i = 1; i < a.length; i++) {
int w = st.get(a[i]);
G.addEdge(v, w);
}
}
}