/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if (nums==null||nums.length==0) {
            return null;
        }
        return getBalancedBST(nums, 0, nums.length-1);
    }
    private TreeNode getBalancedBST(int[] arr,int start,int end) {
        if (start>end) {
            return null;
        }
        TreeNode node = new TreeNode(arr[(start+end)/2]);
        node.left = getBalancedBST(arr, start, (start+end)/2-1);
        node.right = getBalancedBST(arr, (start+end)/2+1, end);
        return node;
    }
}