added assignment 4 ex 2

src/Assignment4/Ex2_Trees.sc

@@ -0,0 +1,22 @@
+sealed abstract class BinaryTree
+case class Leaf(value: Int) extends BinaryTree
+case class Node(left: BinaryTree, right: BinaryTree) extends BinaryTree
+
+def leafSum(tree: BinaryTree): Int = {
+  tree match {
+    case Leaf(value) => value
+    case Node(left, right) => leafSum(left) + leafSum(right)
+  }
+}
+
+def min(a: Int, b: Int): Int = if (a < b) a else b
+def smallest(tree: BinaryTree): Int = {
+  tree match {
+    case Leaf(value) => value
+    case Node(left, right) => min(smallest(left), smallest(right))
+  }
+}
+
+assert(leafSum(Node(Node(Leaf(3), Leaf(8)), Leaf(5))) == 16)
+
+assert(smallest(Node(Node(Leaf(3), Leaf(5)), Leaf(-5))) == -5)