public void solve()
{
Console.WriteLine("solving started");
module_backtrack mb = new module_backtrack(this);
mb.solve();
Console.WriteLine("Solving completed");
}
void solve_backTrack(Board board)
{
Console.WriteLine("hello, Cruel World!");
Console.WriteLine("valid board?: " + board.isValid());
module_backtrack mb = new module_backtrack(board);
mb.solve();
mb.clone_to_original();
Console.WriteLine(mb.original.to_string());
Console.WriteLine("valid : " + mb.original.isValid());
Console.WriteLine("complete : " + mb.original.isComplete());
return;
}