public void TopologicalSort_ValidGraph_SortsCorrectly()
{
// arrange
GraphNode openDoor = new GraphNode("open door");
GraphNode unlockCar = new GraphNode("unlock car");
GraphNode getInCar = new GraphNode("get in car");
GraphNode turnOnEngine = new GraphNode("turn on engine");
GraphNode adjustMirrors = new GraphNode("adjust mirrors");
GraphNode turnOnHeadlights = new GraphNode("turn on headlights");
unlockCar.Paths.Add(openDoor);
openDoor.Paths.Add(getInCar);
getInCar.Paths.Add(adjustMirrors);
getInCar.Paths.Add(turnOnHeadlights);
adjustMirrors.Paths.Add(turnOnEngine);
turnOnHeadlights.Paths.Add(turnOnEngine);
GraphNode[] nodes = new GraphNode[] { adjustMirrors, turnOnHeadlights, openDoor, unlockCar, getInCar, turnOnEngine, };
GraphNavigator navigator = new GraphNavigator();
// act
GraphNode[] topologicalSort = navigator.TopologicalSort(nodes).ToArray();
// assert
Assert.AreEqual(topologicalSort[0], unlockCar);
Assert.AreEqual(topologicalSort[1], openDoor);
Assert.AreEqual(topologicalSort[2], getInCar);
Assert.IsTrue(topologicalSort[3] == adjustMirrors || topologicalSort[3] == turnOnHeadlights);
Assert.IsTrue(topologicalSort[4] == adjustMirrors || topologicalSort[4] == turnOnHeadlights);
Assert.AreEqual(topologicalSort[5], turnOnEngine);
Assert.AreEqual(topologicalSort.Length, 6);
}
public IEnumerable<GraphNode> TopologicalSort(GraphNode[] graph)
{
HashSet<GraphNode> visited = new HashSet<GraphNode>();
Stack<GraphNode> sorted = new Stack<GraphNode>();
foreach (GraphNode node in graph)
{
TopologicalSort(node, visited, sorted);
}
return sorted;
}
private void TopologicalSort(GraphNode node, HashSet<GraphNode> visited, Stack<GraphNode> sorted)
{
if (visited.Contains(node)) return;
visited.Add(node);
foreach (GraphNode n in node.Paths)
{
TopologicalSort(n, visited, sorted);
}
sorted.Push(node);
}