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trees/construct_tree_inorder_preorder.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
+def build_tree(preorder: list[int], inorder: list[int]) -> Optional[TreeNode]:
+        
+        def helper(i_left, i_right, index_map):
+            
+            if i_left > i_right:
+                return None
+            
+            root = TreeNode(preorder.pop(0))
+            index_here = index_map[root.val]
+
+            # this order change from postorder
+            root.left = helper(i_left, index_here - 1, index_map)
+            root.right = helper(index_here + 1, i_right, index_map)
+            
+            return root
+            
+        
+        index_map = {value: index for index, value in enumerate(inorder)}
+        
+        return helper(0, len(inorder) - 1, index_map)
+