public boolean removeEdge(Vertex<T> from, Vertex<T> to) {
Edge<T> e = from.findEdge(to);
if (e == null) return false;
else {
from.remove(e);
return true;
}
}
public boolean addEdge(Vertex<T> from, Vertex<T> to, int cost) throws IllegalArgumentException {
if (!verticesHash.containsKey(from.getName()))
throw new IllegalArgumentException("from is not in graph");
if (!verticesHash.containsKey(to.getName()))
throw new IllegalArgumentException("to is not in graph");
Edge<T> e = new Edge<T>(from, to, cost);
if (from.findEdge(to) != null) return false;
else {
from.addEdge(e);
return true;
}
}