Create construct_tree.py

trees_and_graphs/construct_tree.py

@@ -0,0 +1,25 @@
+# Given two integer arrays inorder and postorder where inorder is the inorder 
+# traversal of a binary tree and postorder is the postorder traversal of the
+# same tree, construct and return the binary tree.
+
+def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:
+        
+        def fill_tree(i_left, i_right, inorder_map):
+            
+            if i_left > i_right:
+                return None
+            
+            val = postorder.pop()
+            root = TreeNode(val)
+
+            index_here = inorder_map[val]
+
+            root.right = fill_tree(index_here + 1, i_right, inorder_map)
+            root.left = fill_tree(i_left, index_here - 1, inorder_map)
+            
+            return root
+
+        inorder_map = {val: index for index, val in enumerate(inorder)}
+  
+        return fill_tree(0, len(inorder) - 1, inorder_map)
+