Refactoring Eight Queens: Step 4

Doing the next refactoring, to get rid of the else, 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)
        return 1;

      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;
    }

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

All the tests pass.

Onto the next refactoring: I see that the nesting is deeper than I like. Let’s add a method, IsSpotUnderAttack, and see if we can get rid of some of that nesting.

Then click Next.