Riverbank - Episode 4: Nessie
(Published on 20. May 2022, 09:26 by henrypijames)
- Normal sudoku: Fill every row, column and marked 3×3 box with the digits 1 to 9 once each.
- River & riverbank: Locate a river (think: classic snake) in the grid, consisting of a one-cell wide, non-looping, non-branching string of orthogonally connected cells, which may not touch itself orthogonally (but may diagonally); each border between a river cell and a non-river cell is a riverbank segment (this precludes the grid edge from being counted as riverbank).
- Riverbank sweeper & sentinel: Each circled cell is a riverbank sweeper, which counts riverbank segments within the (up to 3×3) surrounding cells; each squared cell is a riverbank sentinel, which counts riverbank segments in its row and column combined (see example image).
- No negative constraint: Not all circles and squares are necessarily given. Puzzle
To familiarize yourself with the riverbank ruleset, please consider first checking out the 6×6 introductory puzzle Episode 2: Adobe Illustrator and/or the previous full-size puzzle with only sweeper but no sentinel Episode 3: Watch on the Rhine.
- Download this puzzle as: scalable image (SVG) | bitmap image (PNG) | printable document (PDF).
Note: SVG auto-switches colors depending on light/dark mode in system/browser setting; PDF is in printing-friendly black on white. - Play online on: Penpa+ | CtC App.
- Compare your solve against the walkthrough of this puzzle.
The (real) debut of riverbank sentinel! @Nordy and I have spent close to a hundred hours combined working on this puzzle - and had so much fun doing it! The break-in, mid- and endgame each went through several rounds of significant change, while the ruleset continues to amaze us with its logical width and depth.
Solution code: Row 3 & column 6 (left to right & top to bottom, 18 digits)
Comments
on 24. May 2024, 15:55 by Christounet
Awesome puzzle ! Really tough but clean and fun logic throughout. It takes a while to fully investigate the possible patterns of river shapes and how it affects the sweepers. Having previous experience with snake puzzles certainly helped here ! One needs to be very careful with the sentinel sweeper counting. Thanks :)
on 3. December 2022, 03:32 by Selenotropism
Difficult, but satisfying break in. What follows just as nice unique logic.
on 28. June 2022, 22:36 by lerroyy
Very nice puzzle!
Very hard puzzle, did a lot of counting mistakes, swapping circles and squares and broke the grid a few times. But I finally did it. Thanks henrypijames and nordy!
on 22. June 2022, 23:24 by KNT
Wonderful puzzle! Took me quite a while but I am glad I persevered. Thank you Henry and Nordy! By the way - I am highly appreciative of your inclusion of multiple file formats such as SVGs.
on 7. June 2022, 14:05 by henrypijames
Walkthrough finally up (sorry it took longer than originally planned)
on 7. June 2022, 13:32 by Niverio
This was a very enjoyable experience, even though I broke it like 5 times trying yesterday. Superb puzzle!
on 24. May 2022, 05:37 by henrypijames
Add walkthrough announcement
on 22. May 2022, 23:19 by hepcecob
Challenging all the way through. The break in was awesome. Frustrating but fair puzzle :)
on 20. May 2022, 16:25 by LittleBallOfPurr
Popped some "Gentle Stream Sounds" on Youtube to help me think like a river. Very nicely crafted and clever rule set. Many thanks!
on 20. May 2022, 15:12 by Jesper
Very nice and challenging, thanks!
on 20. May 2022, 09:44 by kolot
This is a very cleverly designed and a quite challenging puzzle. You will learn a lot about this rule set while solving this puzzle.
on 20. May 2022, 09:40 by filuta
This is how I imagine a perfect break-in, the excperience with the ruleset certainly comes in handy with this one. And the sentinels do some amazing work. Really well done!
