using System;

namespace ClassExamples
{
   class SudokuMaker
   {
      public static int[,] createSudoku(int emptyPositions)
      {
         int[,] sudoku = new int[9,9];
         int temp = 0;
         int i,j;
         for (i=0; i<9; i++)
         {
            for (j=0; j<9; j++)
            {
               temp = j + i*3 + (i/3 + 1) + 1;
               sudoku[i,j] = temp - (9 * (temp/9)) + 1;
            }
         }

         Random rand = new Random();
         int removed = 0;
         while (removed < emptyPositions)
         {
            i = rand.Next(9);
            j = rand.Next(9);

            if (sudoku[i,j] > 0)
            {
               sudoku[i,j] = -1;
               removed++;
            }
         }

         return sudoku;
      }

      public static void Main(string[] args)
      {
         int[,] sudoku = createSudoku(40);
         printSudoku(sudoku);
      }

      public static void printSudoku(int[,] sudoku)
      {
         for (int i=0; i<9; i++)
         {
            if (i%3 == 0)
            {
               Console.WriteLine("=============================");
            }
            Console.Write("|| ");

            for (int j=0; j<9; j++)
            {
               if (sudoku[i,j] > 0) {
                  Console.Write(sudoku[i,j]);
               } else {
                  Console.Write(" ");
               }

               if ((j+1)%3 != 0) {
                  Console.Write(" ");
               } else {
                  Console.Write(" || ");
               }
            }
            Console.WriteLine();
         }
         Console.WriteLine("=============================");
      }
   }
}