using System;

public class Program

{

    public static void Main()

    {

        int[,] puzzle = {

    { 9, 8, 7, 6, 5, 4, 3, 2, 1 },

    { 6, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 5, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 0, 0, 0 },

    { 0, 0, 0, 0, 0, 0, 5, 0, 6 }

};

​

if (SolveSudoku(puzzle, 0, 0))

    PrintSudoku(puzzle);

    }

​

public static void PrintSudoku(int[,] puzzle)

{

    Console.WriteLine("+-----+-----+-----+");

​

    for (int i = 1; i < 10; ++i)

    {

        for (int j = 1; j < 10; ++j)

            Console.Write("|{0}", puzzle[i - 1, j - 1]);

​

        Console.WriteLine("|");

        if (i % 3 == 0) Console.WriteLine("+-----+-----+-----+");

    }

}

​

public static bool SolveSudoku(int[,] puzzle, int row, int col)

{

    if (row < 9 && col < 9)

    {

        if (puzzle[row, col] != 0)

        {

            if ((col + 1) < 9) return SolveSudoku(puzzle, row, col + 1);

            else if ((row + 1) < 9) return SolveSudoku(puzzle, row + 1, 0);

            else return true;

        }

        else

        {

            for (int i = 0; i < 9; ++i)

            {

                if (IsAvailable(puzzle, row, col, i + 1))

                {

                    puzzle[row, col] = i + 1;

​

                    if ((col + 1) < 9)

                    {

                        if (SolveSudoku(puzzle, row, col + 1)) return true;

                        else puzzle[row, col] = 0;

                    }

                    else if ((row + 1) < 9)

                    {

                        if (SolveSudoku(puzzle, row + 1, 0)) return true;

                        else puzzle[row, col] = 0;

                    }

                    else return true;

                }

            }

        }

​

        return false;

    }

    else return true;

}

​

private static bool IsAvailable(int[,] puzzle, int row, int col, int num)

{

    int rowStart = (row / 3) * 3;

    int colStart = (col / 3) * 3;

​

    for (int i = 0; i < 9; ++i)

    {

        if (puzzle[row, i] == num) return false;

        if (puzzle[i, col] == num) return false;

        if (puzzle[rowStart + (i % 3), colStart + (i / 3)] == num) return false;

    }

​

    return true;

}

}