Topologically sort a directed acyclic graph (DAG) with cycle detection.
This topological sort can be used to put items in dependency order, where each edge (u, v) has a vertex u that is depended on by v, such that u must come before v.
The result of completing a topological sort is an ordered slice of vertexes, where the position of every vertex in the list is before any of its destination vertexes.
After sorting this graph:
A--> B--> D--> E <---F
| ^ |
| | |
+-------> C <--------+
The following conditions must be true concerning the relative position of the
nodes in the returned list of nodes: A<B, A<C, B<D, D<E, C<D, F<C, F<E. The
slice [F A C B D E] is a correct result.
This implementation uses Kahn's algorithm.
$ go get github.com/gammazero/toposort
sorted, err := Toposort([]Edge{
{"B", "D"}, {"D", "E"}, {"A", "B"}, {"A", "C"},
{"C", "D"}, {"F", "C"}, {"F", "E"}})
if err != nil {
log.Fatal("Toposort returned error:", err)
}
fmt.Println("Sorted correctly:", sorted)