What the hell they think they are doing?
If the question creator didn't tell you what's the relationship between 1-dimensional list and balanced Binary Search Tree, why do you think you can solve that question without any doubt? You naturally know that the tree root is the middle of 1-dimensional list? Never!
So as long as I see, the question creator should give at least 3 examples to clarify the relationship between the 1-dimensional list and the balanced BST.
In that case, we can analysis and solve this problem without any doubt.