From ff3987dffc2aaa7b413e96d77e1ed44070d8f66d Mon Sep 17 00:00:00 2001
From: bt3gl <138340846+bt3gl-cryptographer@users.noreply.github.com>
Date: Tue, 8 Aug 2023 14:32:28 -0700
Subject: [PATCH] Update bt_postorder.py

---
 trees/bt_postorder.py | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/trees/bt_postorder.py b/trees/bt_postorder.py
index e5d8826..d3aa1a1 100644
--- a/trees/bt_postorder.py
+++ b/trees/bt_postorder.py
@@ -4,8 +4,34 @@
 
 def postorder(root) -> list:
         
-  if root is None:
+    if root is None:
       return []
     
-  return postorder(root.left) + postorder(root.right) + [root.val] 
+    return postorder(root.left) + postorder(root.right) + [root.val] 
+        
+
+def postorder_iterative(root) -> list:
+        
+    stack, result = [], []
+    node = root
+    
+    while node or stack:
+
+            while node:
+                if node.right:
+                    stack.append(node.right)
+                stack.append(node)
+                node = node.left
+            
+            node = stack.pop()
+            
+            if stack and node.right == stack[-1]:
+                stack[-1] = node
+                node = node.right
+
+            else:
+                result.append(node.val)
+                node = None
+                
+    return result