Cheryl's Sudoku
(Published on 3. June 2025, 03:50 by Elytron)
Solve it on SudokuPad.
Rules:
- Albert, Bertrand, Carl and David are perfectly logical Sudoku solvers. They are shown the following 4×4 Sudoku grid with these rules:
- Normal 4×4 Sudoku rules apply.
- Digits in cages sum up to the value in the top left and may repeat if allowed by other rules.
- Each solver is privately told the value of one variable:
- Albert is told A, Bertrand is told B, Carl is told C, and David is told D.
- They then have the following conversation:
- Albert: "Nobody here can place any digits yet."
- Bertrand: "Well, now I do."
- Carl: “No one else was told the same number as I was.”
- David: “Someone here knows more digits than I do.”
- After this exchange, one of the four solvers completes the Sudoku.
Can you do the same?
Solution code: Row 1 from left to right followed by the starting letter of the first person who was able to solve the Sudoku (4 digits, 1 letter).
Comments
on 27. July 2025, 00:58 by Exigus
That was really cool. Flawless logic, a bit grindy at the start but then everything started falling into place. Thanks!
on 23. July 2025, 04:42 by Phistomefel
Very fun and unique puzzle! Thanks a lot, Elytron!
on 12. July 2025, 05:04 by TheNineElements
Solve Time: 25:57
I rated this 4/5 difficulty.
This was one of the most interesting & unique puzzles I have ever seen - I will need to check out the referenced puzzle this one was inspired by! This puzzle has a very interesting (and unusual) premise, and the solving logic/approach was totally unexpected and tricky. Everything about this puzzle felt different (in a good way) from any other sudoku I've seen.
I really liked how the structure of the clues (each of the statements made by each solver) led me down a logical solve path, with each new clue leading me down a rabbithole of compounding deductions. It felt like solving a riddle, with just a bit of straightforward classic & killer (w/ repeats) sudoku sprinkled in. The clues were all very engaging, and it was really cool how the "pure" logic (meaning, informal written/spoken logic) interfaced with sudoku geometric & killer cage logic. All the clues/statements were rewarding and worked in totally unexpected ways.
My favorite aspect of the puzzle was probably the very last disambiguation (determining who finally solved the puzzle; and then solving it) - but that whole last idea was absolutely diabolical. The break-in (first clue) was also brilliant and was such a cool idea that really "set the stage" for the rest of the puzzle.
Regarding difficulty, I think that 4* is reasonable. The whole puzzle flowed quite smooth for me once I managed to solve/understand the first clue & begin making pencilmarks. The middle two clues were probably a bit easier than the first, but definitely not trivial. The midgame may have felt a bit easier because the break-in helped me understand "how" the puzzle rules worked - but, either way, that final clue was definitely trickier! The logic itself wasn't too difficult, but I got stuck at the very end of the puzzle for several minutes just re-reading the rules until I asked the right questions. Like mentioned before, I think 4* is fair; my time of 26 minutes for a 4*4 sudoku puzzle definitely reflects that.
I have absolutely no idea how you managed to create & set this puzzle - but thank you for doing so & sharing it here!
on 24. June 2025, 09:29 by konjecture
Beautiful logic
on 13. June 2025, 04:51 by kdkirby
Wow, this is a masterpiece. Sending this to my philosophy professor who works on epistemic logic and problems of common knowledge. Thank you so much!
on 10. June 2025, 02:02 by antiknight
Beautiful idea to put into a Sudoku puzzle!
on 9. June 2025, 13:03 by mscha
Amazing! Didn't think I was going to solve it, but I managed to stay ahead of Simon while watching his CtC solve (with a lot of pausing).
SudokuPad says I solved it in 13:37 (!), but that's because I only opened it once I had a digit to put on there (after at least an hour).
on 7. June 2025, 21:55 by SudokuExplorer
Unbelievable! I’m amazed this solves logically with such vague clues, thanks a tonne for creating this :-)
on 7. June 2025, 17:05 by jwsinclair
Brilliant :)
on 7. June 2025, 10:35 by juggler
Best thing I've solved in ages, what an amazing logic puzzle!
on 6. June 2025, 17:21 by Elytron
A few rewordings to make the rules clearer.
on 6. June 2025, 05:40 by jinkela114514
Hope that this puzzle can be featured on CtC channel.
on 5. June 2025, 15:41 by PjoeterBliep
That certainly wasn't easy and required quite a bit of paper for taking notes!
Wonderful!
It blows my mind that this exists
on 5. June 2025, 08:45 by TannersES
genius！no more word i can say
on 5. June 2025, 07:09 by Crusader175
Absolutely brilliant puzzle and everything can be deduced by logic. Very well constructed puzzle!
on 5. June 2025, 01:15 by blueberrypug
does "nobody knows any digits yet" mean they dont know the specific cell location of a digit, or just the specific digit content of a cage?
Elytron: Yes, it means that they do not know the exact location of any digit, i.e. they cannot place any digits yet.
on 3. June 2025, 20:22 by Enchanter73
This was a great thinking exercise, thank you!
on 3. June 2025, 15:34 by cyddrdrd
Brilliant!!!
on 3. June 2025, 05:52 by xiaoji
Nice logic in this intriguing puzzle. I've learnt the original birthday puzzle, but this puzzle still surprises me a lot.
