public boolean isBalanced_V3(TreeNode root) {
        if (root == null)
            return true;
        int left = getDepth(root.left);
        int right = getDepth(root.right);
        if (Math.abs(left - right) > 1)
            return false;
        else
            return isBalanced_V3(root.left) && isBalanced_V3(root.right);

    }