Getting Possible Values (Sudoku Game)

[brycematheson]

Once again, I'm having trouble with my Sudoku Game. This is the last part and I'm almost there! I just need a little bit of help. According to the rules of Sudoku, there can only be once instance of each value in each column, row, and 3x3 grid. I'm writing a function which will tell you the possible values you can input in each spot. I'm having problems.

What I'm trying to do is write all the values of the row into one array, and then all the values of the column into another array. Then, compare the two arrays and output the numbers that don't exist in either of the two. This is what I have so far:

   //Declare variables
   char letter;
   int number;
   int rowNotPossibles[9];
   int colNotPossibles[9];
   int possibles[] = {1,2,3,4,5,6,7,8,9};

   //Gets letter/number coordinates
   cout << "What are the coordinates of the square: ";
   cin  >> letter >> number;

   //Converts letter to uppercase otherwise
   //ASCII conversion in next step won't work
   letter = toupper(letter);

   //If square is not equal to zero, display "read only" message
   if (sudokuBoard[letter - 65][number - 1] != 0)
   {
      cout << "ERROR: Square \'" << letter << number << "\' is read-only\n";
      cout << "\n";
      getOption(sudokuBoard);
   }
   else
   {
      //Gets the current column and row
      int currentColumn = (letter - 65);
      int currentRow = (number - 1);

      for (int i = 0; i < 9; i++)
      {
         colNotPossibles[i] = sudokuBoard[i][currentColumn];
         rowNotPossibles[i] = sudokuBoard[currentRow][i];
      }

   }
   //Displays the possible values based on the coordinates the user entered
   cout << "The possible values for \'" << letter << number << "\' are: ";

   cout << "\n\n";
   getOption(sudokuBoard);
}

I'm lost. Any help? I'm also absolutely completely and entirely clueless on how to compare it to a 3x3 grid. Any help on that would be greatly appreciated, also. Thank you in advance!

[itsmeandnobodyelse]

The first thing you should do is to check letter and number after input. If the user types wrong coordinates (or small letter for instance) you probably would crash when accessing your table entries.

To check for possible values of a given cell, you simply could make a for loop from 1 to 9 and for each number you make a triple check on row, column and sqare whether the number already occurs. The checks can be done by an additional for loop, e. g. for row check you keep the row index fixed and run the column index and vice versa for column check.

Square is a little bit more tricky cause you need to compute the top-left coordinates of the square from the current row and column. That could be done by using integer division:

int rowTopOfSquare = (currentRow/3) * 3;

The above gives 0 for currentRow = 0,1,2 and 3 for currentRow = 3,4,5 and so on.

Do the same with columnLeftOfSqare.

Then in the check loop running i from 1 to 9 you calculate

row = (rowTopOfSquare + ((i-1)/3); // division gives 0,0,0,1,1,1,2,2,2
col = (columnLeftOfSqare +((i-1)%3); // modulo 3 gives 0,1,2,0,1,2,0,1,2

That way you'll get all coordinates of the given square.

If any of the triple checks finds the i already set you could break the current loop and omit the remaining checks. Only an i which passes all three loops without hit would be a possible number that you can store in a new array of 9.

[brycematheson]

I'm a little confused. As you can tell, I'm a beginner at C++. From the above statement, this is about what I got:

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

         }

      }

Haha. Could you maybe explain it a little bit more? Thank you!

[D_Drmmr]

I'm a little confused. As you can tell, I'm a beginner at C++. From the above statement, this is about what I got:

Haha. Could you maybe explain it a little bit more? Thank you!

Perhaps you should first think about what the program should do. Take an example and work it out on paper. Then try to find a general form of the algorithm you use and work that out. Then check if it works in all cases. Before you've done all that you shouldn't be writing a single line of code.

[itsmeandnobodyelse]

I'm a little confused. As you can tell, I'm a beginner at C++. From the above statement, this is about what I got:

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

         }

      }

Haha. Could you maybe explain it a little bit more? Thank you!

The above nested loops would run 81 cycles, i. e. they were suitable to examine each cell in your sudoku game. Your current q. however asked for the possible numbers for a given empty cell, right? The examination of the whole table won't help for taht, right?

So, you better read my post more thoroughly. It describes what you could do below comment

//Displays the possible values based on the coordinates the user entered

and the description isn't - mainly - C++ code but a verbal description what you could do to find the possible numbers. It is now your task to work out the C++ code for that.