Waiters at Work solver

This is an automatic, deduction-based solver for the Waiters at Work daily puzzle from Layton's Mystery Journey, which as far as I can tell is an original puzzle type for the game. I don't actually find it all that interesting, which is perhaps proven by how a handful of relatively simple deduction rules are enough to solve every puzzle in the game, but I just had an urge to write a solver for it anyway. This is inspired pretty heavily by the excellent SudokuWiki solver.

You can load any of the puzzles from the game and edit the grid manually by left-/right-clicking on the cells. There's some detection of contradictions but it's not super robust, so if you input something that doesn't have a valid solution then you might get garbage output.

For reference, these are the puzzle's rules as given in-game:

• Fill the restaurant floor with diners and dishes
• Diners must sit facing each other
• There must be at least one dish between pairs of diners, but there can't be other diners or plants in the way
• Dishes must always be between diners

The puzzle data is all copied from the game; the specific authors of individual puzzles aren't credited, so here's everyone credited for the daily puzzles: Takemasa Aoki, Fumitaka Abe, Daisuke Arai, Takeshi Iwasaki, Mitsuyuki Okuyama, Mitsuhiro Ogura, Kenji Ono, Nobuki Kashihara, Toshio Karino, Takashi Kawasaki, Yuki Kawabe, Takashi Kiyomi, Sumihiro Kobayashi, Yuichi Saito, Yuma Saito, Nobuyuki Sakamoto, Tomonobu Jiku, Katsuya Suzuki, Satoru Suzuki, Masaru Taguchi, Emiko Takeuchi, Soma Tange, Takayuki Tsushima, Kazuhiro Nakamura, Takahiro Hyakkai, Makoto Furukawa, Hisato Mori, Junki Yamada, Nao Arai, Yoshinao Anpuku, Yuuki Oonuki, Junji Takeuchi, and Toru Mizoguchi.

The source code is lying around over here: https://bitbucket.org/CHz16/waiters-at-work-solver