diff --git a/trees/bst_is_valid.py b/trees/bst_is_valid.py
index ec7a1dc..ebf356e 100644
--- a/trees/bst_is_valid.py
+++ b/trees/bst_is_valid.py
@@ -3,26 +3,14 @@
 # author: bt3gl
 
 
-def is_valid_bst_recursive(root):
-  
-          def is_valid(root, min_val=float(-inf), max_val=float(inf)):
-            if root is None:
-                return True
-        
-            return (min_val < root.val < max_val) and \
-                        is_valid(root.left, min_val, root.val) and \
-                        is_valid(root.right, root.val, max_val)
-        
-      return is_valid(root)
-
-
 def is_valid_bst_iterative(root):
         
-        queue = deque()
-        queue.append((root, float(-inf), float(inf)))
+        queue = deque((root, float(-inf), float(inf)))
         
         while queue:
+          
             node, min_val, max_val = queue.popleft()
+          
             if node:
                 if min_val >= node.val or node.val >= max_val:
                     return False
@@ -32,6 +20,16 @@ def is_valid_bst_iterative(root):
                     queue.append((node.right, node.val, max_val))
         
         return True
+
+
+def is_valid_bst_recursive(root, min_val=float(-inf), max_val=float(inf)):
+            
+        if root is None:
+            return True
+        
+        return (min_val < root.val < max_val) and \
+                  is_valid_bst_recursive(root.left, min_val, root.val) and \
+                  is_valid_bst_recursive(root.right, root.val, max_val)
     
     
 def is_valid_bst_inorder(root):
@@ -41,14 +39,14 @@ def is_valid_bst_inorder(root):
                 return True
             
             inorder(node.left)
-            queue.append(node.val)
+            stack.append(node.val)
             inorder(node.right)
             
-        queue = []
+        stack = []
         inorder(root)
-        for i in range(1, len(queue)):
-            if queue[i] <= queue[i-1]:
+  
+        for i in range(1, len(stack)):
+            if queue[i] <= queue[i - 1]:
                 return False
             
         return True
-