// This class demonstrates how to use "yield return" recursively
public RecursivelyEnumerableBinaryTreeWrapper(BinaryTree <TData> tree)
{
Tree = tree;
}
static void Main(string[] args)
{
// This program shows how to iterate over a binary tree with a non-recursive algorithm.
// The main idea is to show how to write GetNextNode() and GetPrevNode() without the
// benefit of recursion. In a recursive algorithm, the runtime stack keeps some important
// contextual information for us. With a non-recursive algorithm, we don't have the benefit
// of the stack, so we have to do a little more work. See the implementations of
// BinaryTree.GetNextNode() and BinaryTree.GetPrevNode().
var tree = new BinaryTree <string>(StringComparer.Create(System.Globalization.CultureInfo.CurrentCulture, false));
// Note: My Insert() algorithm doesn't guarantee the tree is balanced, but that's not important
// for the purpose of this exercise. I'm merely trying to demonstrate that GetNextNode() and
// GetPrevNode() work as expected.
//
// The nodes are inserted in sorted order.
tree.Insert("One");
tree.Insert("Two");
tree.Insert("Three");
tree.Insert("Four");
tree.Insert("Five");
tree.Insert("Kevin");
tree.Insert("Alias");
tree.Insert("Heavy");
tree.Insert("Murky");
tree.Insert("Added");
tree.Insert("Birch");
tree.Insert("Viva");
tree.Insert("Money");
Console.WriteLine("Iterate Forwards Through Tree");
Console.WriteLine("-----------------------------");
var node = tree.GetFirstNode();
while (node != null)
{
Console.WriteLine(node.Data);
node = tree.GetNextNode(node);
}
Console.WriteLine();
Console.WriteLine("Iterate Backwards Through Tree");
Console.WriteLine("------------------------------");
node = tree.GetLastNode();
while (node != null)
{
Console.WriteLine(node.Data);
node = tree.GetPrevNode(node);
}
Console.WriteLine();
Console.WriteLine("Iterate Through Tree with Recursive Iterator using yield return");
Console.WriteLine("---------------------------------------------------------------");
var recursiveWrapper = new RecursivelyEnumerableBinaryTreeWrapper <string>(tree);
foreach (string val in recursiveWrapper)
{
Console.WriteLine(val);
}
// Using the enumerator's MoveNext() method, we're essentially accomplishing the same
// thing as the non-recursive version of GetNextNode(). In most languages, it isn't
// possible to implement a recursive, manually-controllable enumerator because we need
// a way of returning the next result back to the caller. However, using C#'s
// "yield return" technique, we can accomplish this in an elegant way.
var enumerator = (recursiveWrapper as IEnumerable <string>).GetEnumerator();
Console.WriteLine();
Console.WriteLine("Calling the Enumerator methods manually (without foreach)");
Console.WriteLine("---------------------------------------------------------");
while (enumerator.MoveNext())
{
Console.WriteLine(enumerator.Current);
}
}
