Refactoring Eight Queens: Step 6

Doing the next refactoring, adding PlaceQueen and RemoveQueen methods results in something like:

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 (IsSpotUnderAttack(row, col))
          continue;

        PlaceQueen(row, col);
        count += Solve(row + 1);
        RemoveQueen(row, col);
      }
      return count;
    }
    bool IsSpotUnderAttack(int row, int col) const { return colOccupied[col] || diag1Occupied[row+col] || diag2Occupied[SIZE-row+col-1]; }
    void PlaceQueen (int row, int col)  { board[row][col] = colOccupied[col]  = diag1Occupied[row+col]  = diag2Occupied[SIZE-row+col-1] = true; }
    void RemoveQueen(int row, int col)  { board[row][col] = colOccupied[col]  = diag1Occupied[row+col]  = diag2Occupied[SIZE-row+col-1] = false; }
  public:
    int CountSolutions() { return Solve(); }
  };
}

And again, all the tests still pass.

Let’s get rid of the comment and while we’re at it, the default parameter on the Solve method, since there’s really no need for it.

When that’s done, click Next.