private static void InOrder(LeetCode897TreeNode root)
        {
            if (root == null)
            {
                return;
            }

            InOrder(root.left);
            results.Add(root.val);
            InOrder(root.right);
        }
        public static LeetCode897TreeNode IncreasingBST(LeetCode897TreeNode root)
        {
            InOrder(root);

            var ans = new LeetCode897TreeNode();
            var cur = ans;

            foreach (var item in results)
            {
                cur.right = new LeetCode897TreeNode(item);
                cur       = cur.right;
            }
            return(ans.right);
        }
 public LeetCode897TreeNode(int val = 0, LeetCode897TreeNode left = null, LeetCode897TreeNode right = null)
 {
     this.val   = val;
     this.left  = left;
     this.right = right;
 }