108. Convert Sorted Array to Binary Search Tree

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