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scala/src/main/scala/ch23_binary_tree/BinaryTree.scala

@@ -0,0 +1,39 @@
+package ch23_binary_tree
+
+class Node[T](var data: T, var left: Option[Node[T]], var right: Option[Node[T]])
+
+class BinaryTree[T] {
+
+  def preOrder(root: Option[Node[T]]): String = {
+    val result = new StringBuilder
+
+    if (root.isDefined) {
+      result.append(root.map(_.data.toString).get)
+      result.append(preOrder(root.get.left))
+      result.append(preOrder(root.get.right))
+    }
+    result.mkString
+  }
+
+  def inOrder(root: Option[Node[T]]): String = {
+    val result = new StringBuilder
+
+    if (root.isDefined) {
+      result.append(inOrder(root.get.left))
+      result.append(root.map(_.data.toString).get)
+      result.append(inOrder(root.get.right))
+    }
+    result.mkString
+  }
+
+  def postOrder(root: Option[Node[T]]): String = {
+    val result = new StringBuilder
+
+    if (root.isDefined) {
+      result.append(postOrder(root.get.left))
+      result.append(postOrder(root.get.right))
+      result.append(root.map(_.data.toString).get)
+    }
+    result.mkString
+  }
+}

scala/src/test/scala/ch23_binary_tree/BinaryTreeTest.scala

@@ -0,0 +1,48 @@
+package ch23_binary_tree
+
+import org.scalatest.{BeforeAndAfterEach, FlatSpec, Matchers}
+
+class BinaryTreeTest extends FlatSpec with BeforeAndAfterEach with Matchers {
+
+  /*
+   *         A
+   *        / \
+   *       B   C
+   *      / \ / \
+   *     D  E F  G
+   *
+   */
+  var root:Option[Node[String]] = None
+  val tree = new BinaryTree[String]
+
+  override def beforeEach() {
+    val D = new Node[String]("D", None, None)
+    val E = new Node[String]("E", None, None)
+    val B = new Node[String]("B", Some(D), Some(E))
+    val F = new Node[String]("F", None, None)
+    val G = new Node[String]("G", None, None)
+    val C = new Node[String]("C", Some(F), Some(G))
+    val A = new Node[String]("A", Some(B), Some(C))
+    root = Some(A)
+  }
+
+  override protected def afterEach(): Unit = {
+    root = None
+  }
+
+  behavior of "BinaryTreeTest"
+
+  it should "postOrder" in {
+    tree.postOrder(root) should equal("DEBFGCA")
+  }
+
+  it should "inOrder" in {
+    tree.inOrder(root) should equal("DBEAFCG")
+  }
+
+  it should "preOrder" in {
+    tree.preOrder(root) should equal("ABDECFG")
+  }
+
+
+}