bool isSafe(int[,] board, int row, int col)
        {
            int i, j;

            /* Check this row on left side */
            for (i = 0; i < col; i++)
                if (board[row, i] == 1)
                    return false;

            /* Check upper diagonal on left side */
            for (i = row, j = col; i >= 0 && j >= 0; i--, j--)
                if (board[i, j] == 1)
                    return false;

            /* Check lower diagonal on left side */
            for (i = row, j = col; j >= 0 && i < 8; i++, j--)
                if (board[i, j] == 1)
                    return false;

            return true;
        }

        /* A recursive utility function  
        to solve N Queen problem */
       bool solveNQUtil(int[,] board, int col)
        {
            /* base case: If all queens are placed  
            then return true */
            if (col == 8)
            {
               // printSolution(board);
                for (int i = 0; i < 8; i++)
                {
                    for (int j = 0; j < 8; j++)
                    {
                        if(board[i,j]==1)
                        Matrix[i][j].BackgroundImage = hinhconco1;                                                                       
                    }
                }
                return true;
            }

            /* Consider this column and try placing  
            this queen in all rows one by one */
            bool res = false;
            for (int i = 0; i < 8; i++)
            {
                /* Check if queen can be placed on  
                board[i,col] */
                if (isSafe(board, i, col))
                {
                    /* Place this queen in board[i,col] */
                    board[i, col] = 1;

                    // Make result true if any placement  
                    // is possible  
                    res = solveNQUtil(board, col + 1) || res;

                    /* If placing queen in board[i,col]  
                    doesn't lead to a solution, then  
                    remove queen from board[i,col] */
                    board[i, col] = 0; // BACKTRACK  
                }
            }

            /* If queen can not be place in any row in  
                this column col then return false */
            return res;
        }