def tree_from_traversals(preorder, inorder):

if len(preorder) != len(inorder):

raise ValueError("traversals must have the same length")

if set(preorder) != set(inorder):

raise ValueError("traversals must have the same elements")

if len(set(preorder)) != len(preorder) != len(set(inorder)):

raise ValueError("traversals must contain unique items")

if not preorder:

return {}

value = preorder.pop(0)

index = inorder.index(value)

left_inorder, right_inorder = inorder[:index], inorder[index+1:]

left_preorder = [x for x in preorder if x in left_inorder]

right_preorder = [x for x in preorder if x in right_inorder]

left = tree_from_traversals(left_preorder, left_inorder)

right = tree_from_traversals(right_preorder, right_inorder)

return {"v": value, "l": left, "r": right}