public void TopologicalSort_Test()
        {
            var G = new Digraph(4);

            G.AddEdge(3, 2);
            G.AddEdge(3, 1);
            G.AddEdge(1, 0);
            G.AddEdge(2, 0);
            var DFO    = new TopologicalSort(G);
            var actual = new List <int>(DFO.GetTopologicalySorted());

            Assert.AreEqual(3, actual[0]);
            Assert.AreEqual(0, actual[3]);
        }