public static void Test()
{
Solution s = new Solution();
int?[] a4 = new int?[] { 3 };
int?[] a5 = new int?[] { 1, 2, 3, 4, 5, 6, null, null, null, 7, 8 };
TreeNode root = new TreeNode(a5[0].GetValueOrDefault());
ProduceTreeNode(a5, a5.Length, 0, root);
int?[] a6 = new int?[] { 1, 2, 3, 4, 5, 6, null, null, null, 7, 8 };
TreeNode root2 = new TreeNode(a5[0].GetValueOrDefault());
ProduceTreeNode(a6, a6.Length, 0, root2);
//a4.PrintList();
Console.WriteLine(s.FlipEquiv(root, root2) + " is true");
}