[Featurette] Added merging two BSTs.

Author: exterkamp

structures/binary_search_tree.py

@@ -49,3 +49,23 @@ def recur(node):
                 recur(node.right)
         recur(self.head)
         return output
+
+    def merge(self, tree):
+
+        def mergeOntoT1(t1, t2):
+            if not t1:
+                return t2
+            if not t2:
+                return t1
+            
+            t1.value += t2.value
+            
+            # look left
+            t1.left = mergeOntoT1(t1.left, t2.left)
+            
+            # look right
+            t1.right = mergeOntoT1(t1.right, t2.right)
+            
+            return t1
+        
+        mergeOntoT1(self.head, tree.head)

tests/test_bst.py

@@ -66,3 +66,19 @@ def test_search(self):
         self.assertEqual(None, tree.search(87))
 
         self.assertEqual(3, tree.search(3).value)
+
+    def test_merge(self):
+
+        tree = self.make_simple_tree()
+
+        tree2 = BinarySearchTree()
+
+        tree2.insert(5)
+        tree2.insert(9)
+        tree2.insert(10)
+
+        tree.merge(tree2)
+
+        self.assertEqual(17, tree.head.value)
+        self.assertEqual(27, tree.search(27).value)
+        self.assertEqual(42, tree.search(42).value)