Implement exercise binary-search-tree (#773)

exercises/binary-search-tree/example.py

@@ -0,0 +1,61 @@
+from collections import deque
+
+
+class TreeNode(object):
+    def __init__(self, value):
+        self.value = value
+        self.left_node = None
+        self.right_node = None
+
+    def __str__(self):
+        return str(self.value)
+
+
+class BinarySearchTree(object):
+    def __init__(self):
+        self.root = None
+
+    def add(self, value):
+        if(self.root is None):
+            self.root = TreeNode(value)
+        else:
+            inserted = False
+            cur_node = self.root
+
+            while not inserted:
+                if(value <= cur_node.value):
+                    if(cur_node.left_node):
+                        cur_node = cur_node.left_node
+                    else:
+                        cur_node.left_node = TreeNode(value)
+                        inserted = True
+                elif(value > cur_node.value):
+                    if(cur_node.right_node):
+                        cur_node = cur_node.right_node
+                    else:
+                        cur_node.right_node = TreeNode(value)
+                        inserted = True
+
+    def search(self, value):
+        cur_node = self.root
+        found = False
+        while not found:
+            if(cur_node is None):
+                return None
+            elif(value < cur_node.value):
+                cur_node = cur_node.left_node
+            elif(value > cur_node.value):
+                cur_node = cur_node.right_node
+            elif(value == cur_node.value):
+                return cur_node
+
+    def list(self):
+        elements = deque()
+        self.trav_inorder(self.root, elements)
+        return elements
+
+    def trav_inorder(self, node, elements):
+        if(node is not None):
+            self.trav_inorder(node.left_node, elements)
+            elements.append(node.value)
+            self.trav_inorder(node.right_node, elements)