How do you build a binary tree from preorder and inorder traversals?

Question presented to candidate: "I give you two arrays: the preorder and the inorder traversal of a binary tree whose values are all distinct. Write a Python function that rebuilds the tree and returns its root."

What a strong answer should cover:

• Preorder's first value is the root; finding that value in inorder splits the remaining values into the left subtree (before it) and the right subtree (after it).
• Recurse on the two parts; the left subtree's preorder comes first, so build left before right while consuming preorder with one moving index.
• A value → index hash map makes each split O(1), giving O(n) total; a linear search per node is O(n²) on a skewed tree.
• Pass index ranges instead of copying sub-arrays.
• Why the values must be distinct (duplicates make the answer ambiguous) and why preorder + postorder alone is not enough in general.
• Python specifics: a dict comprehension for the index map, nonlocal for the shared preorder index, and why inorder.index(...) plus slicing (preorder[1:mid + 1]) quietly makes it O(n²).

Clarifying questions expected:

• Are all values distinct, and are the two arrays guaranteed to describe the same tree?
• How large can n be (is recursion depth a concern)?

Code / implementation expected: Yes — a recursive helper over inorder index ranges with a dict for positions, in Python 3.