Added max method

Author: dosart

Diff for: binary_search_tree/binary_serch_tree.py

@@ -70,6 +70,20 @@ def min(self):
             cur = cur.left
         return cur.key
 
+    def max(self):
+        """Return min key(iterative version).
+
+        Returns:
+            key: min key in tree
+        """
+        if self.is_empty():
+            return None
+
+        cur = self._root
+        while cur.right:
+            cur = cur.right
+        return cur.key
+
     def _add(self, key, value):
         """Add the given key and object to tree(iterative version).