Construct Binary Tree from Preorder and Inorder Traversal

def buildTree(preorder, inorder):
    inorder_map = {val: idx for idx, val in enumerate(inorder)}
    pre_idx = 0
    
    def build(left, right):
        nonlocal pre_idx
        if left > right:
            return None
            
        root_val = preorder[pre_idx]
        root = TreeNode(root_val)
        pre_idx += 1
        
        mid = inorder_map[root_val]
        root.left = build(left, mid - 1)
        root.right = build(mid + 1, right)
        return root
        
    return build(0, len(inorder) - 1)