**TriDoku**! It’s a great puzzle-type but for some reason it’s very rarely seen in the Sudoku world. I want to change that! Even though it may not appear obvious, there are 81 cells in this puzzle. And there are 9 nonets. Just like in your ordinary Sudokus. But there aren’t 9 rows and 9 columns. Why? Because the puzzle is

**triangular**!

**The rules:**1. There are 9 nonets in forms of triangles. These are drawn with thick lines. All must contain all numbers 1-9. 2. Each edge of the big triangle contains 9 numbers – again, no repeats there either. These cells are shaded in DARK GRAY. 3. There is an INNER triangle, shaded in LIGHT GRAY. Each side of the inner triangle contains 9 numbers. No repeats on those sides, please. 4. And finally: two cells that are touching each other must not contain the same number! Make sure you use this rule! Each cell is touching up to 12 other cells! Be careful! All solving techniques come from classic Sudoku. Use naked and hidden singles and subsets in nonets and edges. Use interactions between the nonets and the corresponding edges. But finally, you will have to use:

**the hexagon rule!**The Hexagon rule comes directly from rule number 4. Since two touching cells cannot contain the same numbers, then a group of cells that are ALL touching each other cannot contain any repeats. Simple? Yes. Well then, each hexagon (6 cells pointing to each other) must not contain duplicates, so you CAN use the subsets solving technique, but be careful, there are 6 cells and 9 possible numbers! Some of the techniques I will explain in detail in the coming days. Now, lets see the puzzle! Oh, and one quick note: 3 cells are marked half dark gray half light gray. They are not split in any way, they contain one number, but they belong to both an outside edge and an inner edge, so I marked them this way.

**TriDoku**for Friday, February 12, 2010. Difficulty:

**THINKER**

(click to download or right-click to save the image!) | |

**To see the solution to this puzzle**click here

Comments? Questions? Please!

## 6 Comments

Neat! Took me about 10 minutes for this one, so I’m not sure that it merits thinker status (at least based on my time for other thinkers). But it’s definitely tricky and a very cool variation!

I liked the first one because of the novelty, but I solved it pretty quickly.

If you want to continue publishing this kind of puzzles, I think they have to be more difficult.

Anyway, I prefer jigsaw or outside.

nice,I think my nose will bleed by answering this one.

Learning should be a joy and full of excitement. It is life’s greatest adventure; it is an illustrated excursion into the minds of the noble and the learned. – Taylor Caldwell

Hi! I’m addicted to Tridoku but can’t find many books on them… Are you planning on coming out with another? I’d definitely buy it!

Annemarie, there are some tridokus in the Sudoku Variations book. I might publish a new volume of just Tri Doku, but not sure when.

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[…] Killer TriDoku puzzles: all standard rules of Killer Sudoku apply + of course the TriDoku rules. […]

[…] For those who are still unfamiliar with this type of triangular Sudoku variation puzzle, please refer to the introductory article. […]

[…] Also, as a special gift and to make it up to you, I have prepared a brand new variant – Jigsaw TriDoku. I think the puzzle is self-explanatory. It is a hybrid between Jigsaw Sudoku and TriDoku. Make sure to use the hexagon rule which can be found in the TriDoku introductory article. […]

[…] as a special gift and to make it up to you, I have prepared a brand new variant – Jigsaw TriDoku. I think the puzzle is self-explanatory. It is a hybrid between Jigsaw Sudoku and TriDoku. Make […]

[…] Tridoku […]