Add binary_tee example

bin_tree/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "bin_tree"
+version = "0.1.0"
+authors = ["Timothy Warren <twarren@nabancard.com>"]
+edition = "2018"
+
+[dependencies]

bin_tree/src/main.rs

@@ -0,0 +1,46 @@
+#[derive(Debug)]
+enum BinaryTree<T> {
+    Empty,
+    NonEmpty(Box<TreeNode<T>>)
+}
+
+#[derive(Debug)]
+struct TreeNode<T> {
+    element: T,
+    left: BinaryTree<T>,
+    right: BinaryTree<T>
+}
+
+impl<T: Ord> BinaryTree<T> {
+    fn add(&mut self, value: T) {
+        match *self {
+            BinaryTree::Empty => *self = BinaryTree::NonEmpty(Box::new(TreeNode {
+                element: value,
+                left: BinaryTree::Empty,
+                right: BinaryTree::Empty,
+            })),
+            BinaryTree::NonEmpty(ref mut node) => {
+                if value <= node.element {
+                    node.left.add(value);
+                } else {
+                    node.right.add(value);
+                }
+            }
+        }
+    }
+}
+
+fn main() {
+    let mut tree = BinaryTree::Empty;
+    tree.add("Mercury");
+    tree.add("Venus");
+    tree.add("Earth");
+    tree.add("Mars");
+    tree.add("Jupiter");
+    tree.add("Saturn");
+    tree.add("Uranus");
+    tree.add("Neptune");
+    tree.add("Pluto");
+
+    println!("Tree: {:?}", tree);
+}