Given the `root` of a binary search tree, return a balanced binary search tree with the same node values. If there is more than one answer, return any of them.

A binary search tree is balanced if the depth of the two subtrees of every node never differs by more than `1`.

Example 1:

    Input: root = [1,null,2,null,3,null,4,null,null]
    Output: [2,1,3,null,null,null,4]
    Explanation: This is not the only correct answer, [3,1,4,null,2] is also correct.

Example 2:

    Input: root = [2,1,3]
    Output: [2,1,3]

Constraints:

- The number of nodes in the tree is in the range `[1, 104]`.
- `1 <= Node.val <= 105`