Saturday, 14 January 2012

Puzzle #86: Yajilin; Toroidal

I always liked the toroidal idea for loop puzzles. As I understood from Mathgrant's post Nikoli has published a Toroidal Yajilin too. I was somewhat curious how the clue execution worked. I spend a while considering if it was appropriate to let the clues end on the non-existing edge of the grid. But I figured the puzzle should actually be able to be posted on a torus, so the clues have to point past edges.
I made a few of them to test out how to best construct them. This was the easiest to come out of it. I figured I should first post this one for a change as a lot of times I introduce something new with a (too) hard puzzle. It's still tricky to solve because of the toroidal nature. Especially the deductions that span over the edges can be hard to see. But I didn't really see how to avoid that.

Rules for Yajilin

In this puzzle the grid is toroidal. This means the loop can pass through edges and come out on the other side. The clues also pass through the edge. This means each horizontal arrow sees the whole row and each vertical arrow sees the whole column.

Alternate image

Click to enlarge


  1. Re the over the edge deductions, a slightly more helpful presentation I've seen is to have another copy of the leftmost column on the right and so on bordering the grid.

  2. Yeah, I had seen that way. I added an extra image with such a presentation now.

  3. i think the arrows do not make any sense in toroidal yajilin(if you description of the rules is correct), except that the horizontal/vertical nature need to be depicted using straight lines.

    1. They're just there to keep the normal layout so people recognise the genre.It seems a bit silly to change the layout if they mean the same thing.

  4. I am sure it makes a lot of sense to make the arrows bidirectional if you really want to retain the arrows.A single arrow is meaningful in yajilin only.