/**
* Initializes a new edge-weighted digraph that is a deep copy of {@code G}.
*
* @param G the edge-weighted digraph to copy
*/
public EdgeWeightedDigraph(EdgeWeightedDigraph G) {
this(G.V());
this.E = G.E();
for (int v = 0; v < G.V(); v++)
this.indegree[v] = G.indegree(v);
for (int v = 0; v < G.V(); v++) {
// reverse so that adjacency list is in same order as original
Stack<DirectedEdge> reverse = new Stack<DirectedEdge>();
for (DirectedEdge e : G.adj[v]) {
reverse.push(e);
}
for (DirectedEdge e : reverse) {
adj[v].add(e);
}
}
}
/**
* Determines whether the edge-weighted digraph {@code G} has a
* topological order and, if so, finds such a topological order.
* @param G the digraph
*/
public TopologicalX(EdgeWeightedDigraph G) {
// indegrees of remaining vertices
int[] indegree = new int[G.V()];
for (int v = 0; v < G.V(); v++) {
indegree[v] = G.indegree(v);
}
// initialize
ranks = new int[G.V()];
order = new Queue<Integer>();
int count = 0;
// initialize queue to contain all vertices with indegree = 0
Queue<Integer> queue = new Queue<Integer>();
for (int v = 0; v < G.V(); v++)
if (indegree[v] == 0) queue.enqueue(v);
while (!queue.isEmpty()) {
int v = queue.dequeue();
order.enqueue(v);
ranks[v] = count++;
for (DirectedEdge e : G.adj(v)) {
int w = e.to();
indegree[w]--;
if (indegree[w] == 0) queue.enqueue(w);
}
}
// there is a directed cycle in subgraph of vertices with indegree >= 1.
if (count != G.V()) {
order = null;
}
assert check(G);
}