Completed s30 Trees-2

btfrominandpostordtrav.py

@@ -0,0 +1,34 @@
+class Solution:
+    def buildTree(self, inorder, postorder):
+
+        inorder_map = {}
+
+        for i, val in enumerate(inorder):
+            inorder_map[val] = i
+
+        self.idx = len(postorder) - 1
+
+        def dfs(left, right):
+            if left > right:
+                return None
+
+            # Root is at the end of postorder
+            root_val = postorder[self.idx]
+            self.idx -= 1
+
+            root = TreeNode(root_val)
+
+            mid = inorder_map[root_val]
+
+            # IMPORTANT:
+            # Build right subtree first
+            root.right = dfs(mid + 1, right)
+
+            root.left = dfs(left, mid - 1)
+
+            return root
+
+        return dfs(0, len(inorder) - 1)
+
+    # TC - O(n)
+    # SC - O(n) because of inorder Hashmap and recursion stack O(h)

sumroottoleaf.py

@@ -0,0 +1,19 @@
+class Solution:
+    def sumNumbers(self, root):
+
+        def dfs(node, current_sum):
+            if not node:
+                return 0
+
+            current_sum = current_sum * 10 + node.val
+
+            # leaf node
+            if not node.left and not node.right:
+                return current_sum
+
+            return dfs(node.left, current_sum) + dfs(node.right, current_sum)
+
+        return dfs(root, 0)
+
+    # TC - O(n)
+    # SC - O(h) - recursion stack