Add threaded_binary_tree.dart

Author: happy-san

Diff for: lib/trees/threaded_binary_tree.dart

@@ -0,0 +1,45 @@
+import 'adt/binary_tree_adt.dart';
+import 'binary_tree.dart';
+
+/// Data structure similar to [BinaryNode], differs in having two boolean values
+///  [leftIsThread] and [rightIsThread] to determine whether [left] and [right]
+///  are threads or point to a child instead.
+class ThreadedBinaryNode<V extends Comparable>
+    extends BinaryNodeADT<ThreadedBinaryNode, V> {
+  V value;
+
+  /// Stores if [left] is a thread.
+  bool leftIsThread;
+
+  /// Stores if [right] is a thread.
+  bool rightIsThread;
+}
+
+/// A [BinaryTree] is threaded by making all [right] pointers that would
+///  normally be null point to the in-order successor of the node
+///  (if it exists), and all [left] pointers that would normally be null point
+///  to the in-order predecessor of the node.
+class ThreadedBinaryTree<V extends Comparable>
+    extends BinaryTreeADT<ThreadedBinaryNode, V> {
+  ThreadedBinaryNode root;
+
+  @override
+  void add(V value) {
+    throw UnimplementedError();
+  }
+
+  @override
+  void delete(V value) {
+    throw UnimplementedError();
+  }
+
+  @override
+  List<V> inOrder() {
+    throw UnimplementedError();
+  }
+
+  @override
+  List<V> preOrder() {
+    throw UnimplementedError();
+  }
+}