[leetcode] Convert Sorted Array to Binary Search Tree

public class Solution {
    public TreeNode sortedArrayToBST(int[] num) {
        return toBST(num,0,num.length);
    }
    private TreeNode toBST(int[] num, int from, int to){
        if(to-from<=0)
            return null;
        int mid=(from+to)/2;
        TreeNode root = new TreeNode(num[mid]);
        root.left=toBST(num,from,mid);
        root.right=toBST(num,mid+1,to);
        
        return root;
    }
}