Hmmm... I think about it. To be honest, I have no pain putting *all* methods of Configuration, Board, CheatSheet and MineSweeper into one class; but I thought it would be good to separate concerns.
The responsibility of the Configuration is to know the format of the input file and to parse it.
The responsibility of the CheatSheet is to know the format of the output file and to construct it.
The responsibility of the Board is to know the rules of "MineSweeper" and to perform the logical transformation.
The responsibility of MineSweeper is to coordinate all.
File input / output and the main() function is not yet implemented.