108. Convert Sorted Array to Binary Search Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        int len = nums.length;
        if(len == 0) return null;
        TreeNode ans = toBST(nums,0,len);
        return ans;
    }
    private TreeNode toBST(int[] nums, int start, int end) {
        if(start == end) return null;
        int mid = start + (end - start)/2;
        TreeNode root = new TreeNode(nums[mid]);
//        System.out.println("test");
        root.left = toBST(nums,start,mid);
//        System.out.println("test2");
        root.right = toBST(nums,mid+1,end);
//        System.out.println("test23");
        return root;
    }
}