108. Convert Sorted Array to Binary Search Tree

 1 class Solution {
 2     public TreeNode sortedArrayToBST(int[] nums) {
 3          return nums.length==0? null : ToBST(nums,0,nums.length-1);
 4         
 5         
 6     }
 7     public TreeNode ToBST(int[] nums,int lo,int hi) {
 8         if(lo>hi) return null;
 9          int mid = (lo+hi)/2;
10          TreeNode root = new TreeNode(nums[mid]);
11          root.left = ToBST(nums,lo,mid-1);
12          root.right = ToBST(nums,mid+1,hi);
13          
14         return root;
15         
16     }
17 }