Refactoring Eight Queens: Step 3

Doing that first refactoring, that is, removing numSolns, results in code something like this:

namespace Eight
{
  template <int SIZE> class Queens
  {
    bool board[SIZE][SIZE]={false}, colOccupied[SIZE]={false}, diag1Occupied[SIZE*2 - 1]={false}, diag2Occupied[SIZE*2 - 1]={false};

    int Solve(int row = 0) // assumes all rows before "row" have correctly-placed queens so far
    {
      if (row < SIZE)
      {
        int count = 0;
        for (int col=0; col<SIZE; col++)
        {
          if (!colOccupied[col])
          {
            int diag1 = row + col;
            if (!diag1Occupied[diag1])
            {
              int diag2 = SIZE - row + col - 1;
              if (!diag2Occupied[diag2])
              {
                board[row][col] = colOccupied[col] = diag1Occupied[diag1] = diag2Occupied[diag2] = true;
                count += Solve(row + 1);
                board[row][col] = colOccupied[col] = diag1Occupied[diag1] = diag2Occupied[diag2] = false;
              }
            }
          }
        }
        return count;
      }
      else
      {
        return 1;
      }
    }

  public:
    int CountSolutions() { return Solve(); }
  };
}

The tests still pass.

What next? Well, one of the rules found in Jeff Bay’s “Object Calisthenics” document says you can use an if but not an else. It took me a year to figure out why that was a good idea, but let’s go with Bay’s idea right now.

Let’s refactor to get rid of that else, and then click Next.