Create Balanced BST from sorted array

CreateBalancedBST.java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] num) {
        
        return helper(num, 0, num.length - 1);
        
    }
    
    public TreeNode helper(int[] arr, int left, int right){
        if (left > right) return null;
        
        int mid = (left + right) / 2;
        TreeNode node = new TreeNode(arr[mid]);
        node.left = helper(arr, left, mid-1);
        node.right = helper(arr, mid+1, right);
        
        return node;
    }
}