diff --git a/build_with_postorder_inorder.py b/build_with_postorder_inorder.py
new file mode 100644
index 00000000..e74ae560
--- /dev/null
+++ b/build_with_postorder_inorder.py
@@ -0,0 +1,37 @@
+# Time Complexity: O(n)
+# Space Complexity: O(n) 
+# Did this code successfully run on Leetcode : Yes
+
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+class Solution(object):
+    def buildTree(self, inorder, postorder):
+        """
+        :type inorder: List[int]
+        :type postorder: List[int]
+        :rtype: Optional[TreeNode]
+        """
+        hmap={}
+        self.rootindex=len(postorder)-1
+        for i in range(len(inorder)):
+            hmap[inorder[i]]=i
+
+        def helper(in_st,in_end):
+            if (in_st>in_end): 
+                return None
+
+            rootval=postorder[self.rootindex]
+            in_root_idx=hmap[rootval]
+            root = TreeNode(rootval)
+            self.rootindex-=1
+            root.right = helper(in_root_idx+1,in_end)
+            root.left = helper(in_st,in_root_idx-1)
+
+            return root
+
+
+        return helper(0,len(postorder)-1)
\ No newline at end of file
diff --git a/sum_root_to_leaf.py b/sum_root_to_leaf.py
new file mode 100644
index 00000000..dc72a7d8
--- /dev/null
+++ b/sum_root_to_leaf.py
@@ -0,0 +1,30 @@
+# // Time Complexity : O(n)
+# // Space Complexity : O(h) where h is the height of the tree, for recursive stack space
+# // Did this code successfully run on Leetcode : Yes
+
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def sumNumbers(self, root):
+        """
+        :type root: Optional[TreeNode]
+        :rtype: int
+        """
+        self.res=0
+
+        def helper(root,cur):  
+            if root == None: return          
+            cur=cur*10 + root.val
+            if root.left==None and root.right==None:
+                self.res+=cur
+                return
+            helper(root.left,cur)
+            helper(root.right,cur)
+
+        helper(root,0)
+
+        return self.res