private static void SolveIncompleteClassic()
        {
            SudokuBoard board = SudokuFactory.ClassicWith3x3Boxes(new[]
            {
                "...84...9",
                "..1.....5",
                "8...2.46.", // Removed a "1" on this line
                "7.8....9.",
                ".........",
                ".5....3.1",
                ".2491...7",
                "9.....5..",
                "3...84..."
            });

            CompleteSolve(board);
        }
        private static void SolveClassic()
        {
            SudokuBoard board = SudokuFactory.ClassicWith3x3Boxes(new[]
            {
                "...84...9",
                "..1.....5",
                "8...2146.",
                "7.8....9.",
                ".........",
                ".5....3.1",
                ".2491...7",
                "9.....5..",
                "3...84..."
            });

            CompleteSolve(board);
        }