// The 8-queens game

class Queen {

   int row;
   int column;

  public Queen () {
     row = 99;
     column = 88;
  }

   public Queen (int r, int c) {
     row = r;
     column = c;
   }

   public String toString () {
     String result = "";
     result = result + "(" + row + ", " + column + ")";
     return result;
  }
  
}


class QueensGame {
  
   public static void main (String[] args) {

     Queen[] board = new Queen[8];
     for (int i = 0; i < 8; i++)
        board[i] = new Queen();

     print (board);
      
     play (board, 0);

     print (board);
     

   } // end main


   static boolean play (Queen[] board, int row) {
    
      if (row == 8)
         return true;
   
      for (int column = 0; column != 8;  column++) {

         if (! conflict(board, row, column))  {
             
             addQueen(board, row, column);

             if (play (board, row + 1))  //Proceed to next row             
                   return true; 
             removeQueen(board);
         }        
         
       }        
       return false;

   } // end play

   static Queen[] addQueen (Queen[] board, int row1, int column1) {

      int i = 0;
      while (board[i].row != 99)
          i = i + 1;
      board[i] = new Queen (row1, column1);
      return board;

   }


   static Queen[] removeQueen (Queen[] board) {

      int i = 0;
      while (board[i].row != 99)
          i = i + 1;
      board[i-1] = new Queen ();
      return board;

   }

   static Queen[] print (Queen[] board) {

     for (int i = 0; i < 8; i++) 
       System.out.print (board[i] + "   ");
     System.out.println();
     return board;
   }


   // Method, conflict, checks if a queen can be added in a specified position

   static boolean conflict (Queen[] board, int row, int column) {

     for (int i = 0; i < 8; i++) {

        int queenrow = board[i].row;
        int queencolumn = board[i].column;

        if (threat (row, column, queenrow, queencolumn))
           return true;
     }
 
     return false;
   } // end conflict

   // Method, threat, checks if two queens threaten each other

   static boolean threat (int row1, int column1, int row2, int column2) {


     boolean result = (row1 == row2 || column1 == column2 || 
                (row1 - column1) == (row2 - column2) ||
                (row1 + column1) == (row2 + column2));

     return result;


   } // end threat


} // end class