anchor.diff:    final int cols;
     final int rows;
     final List<bool> _squares;
  +  final List<int> _adjacents;
   
     int _toFindCount;
   
  
positive.code: 
    int getAdjacent(int x, int y) {
      final i = _getIndex(x, y);
      return null;
    }
  
    int _getIndex(int x, int y) {
  
negative.code:       }
      }
      assert(count == mineCount);
  
      _adjacents.insertRange(0, _squares.length);
    }
  
    bool isMine(int x, int y) {
  