C# How can detect cyclic references? -

for 1 given instance of treelist, how can check whether or not instance of treelist, added first treelist, contains (possibly indirect) reference first treelist (which create cyclic reference)?

for example:

treelist t1 = new treelist(); treelist t2 = new treelist(); treelist t3 = new treelist(); t1.add(t2); t2.add(t3); t3.add(t1); 

because when iterrate through stuck in loop, because after t3 t1. how can check if 1 included in order.

class treelist {     public string name { get; set; }     list<treelist> items = new list<treelist>();     public readonlycollection<treelist> items     {         { return items.asreadonly(); }     }      public treelist(string name)     {         this.name = name;     }      public void add(string item)     {         items.add(new treelist(item));     }     public void add(treelist subtree)     {         items.add(subtree);     }     public override string  tostring()     {         return name;     } } 

i think these methods work:

public bool containsrecursively(treelist node) {     foreach (treelist child in items)         if (child == node || child.containsrecursively(node))             return true;      return false; } public void add(treelist tree) {     if (this == tree) return; // tree 'tree', don't add ourselves!     if (this.containsrecursively(tree)) return; // 'tree' in tree     if (tree.containsrecursively(this)) return; // tree in 'tree'     items.add(tree); }