Given a sorted (increasing order) array with unique integer elements, write an algo­rithm to create a binary search tree with minimal height.

Example:

Given sorted array: [-10,-3,0,5,9],



One possible answer is: [0,-3,9,-10,null,5]，which represents the following tree: 



          0 

         / \ 

       -3   9 

       /   / 

     -10  5