Flashback #12 – Shape Sudoku

My last puzzle for this set of flashbacks is Shape Sudoku. Shape Sudoku is near the top of my list of favourite Sudoku variants. I discovered this type in Mutant Sudoku by Wei-Hwa Huang and Thomas Snyder. The world needs more books like this! The pieces fit to spell out “24 HPC” on the grid. I’ve seen this particular puzzle in several instruction booklets long after 2011, sometimes unaccredited.

Shape Sudoku – Decide how each piece fit into the sudoku grid. Pieces can be rotated but not reflected. Then solve the sudoku in the usual manner.

Budapest, November 2011

Budapest, November 2011

3rd LMI Puzzle Marathon

LMI continues its great tradition for the third year with their third Puzzle Marathon. You have from now until the 2nd of March to complete 10 gigantic puzzles but only your best 8 will count towards your results. This year I provided one of the puzzles, I can’t believe it has been more than 2 years since I wrote a puzzle for LMI.

Here are the 10 puzzles to keep you busy for the next 10 days:

4×4 Sudoku by Rohan Rao
KakurOH by Me!
Yajilin by Ravi Kumar
Mini Coral by Bernhard Seckinger

Statue Park by Palmer Mebane
Scrabble by Nikola Zivanovic
Araf by Yuki Kawabe
Nanro by Salih Alan

Turning Fences by Bram de Laat
Heyawake by Tom Collyer

Have fun!

Flashback #11 – Yajilin

This is a surprise Yajilin where the puzzle played out on an irregular grid. I was going to include a sentence in the instructions about how clues affect regions beyond a gap. But that would’ve spoiled the surprise. Having a 3 pointing to just 3 squares should be explanatory enough. These two Yajilins aren’t too hard but not too trivial either, just how I like my puzzles to be.

Yajilin – Draw a single closed loop passing through all the cells in the grid. In addition to the numbered cells, there will  be some blackened cells that the loop will not visit. The numbered cells indicate the number of black squares in that direction. Black squares cannot be adjacent to each other.

Budapest, November 2011

Budapest, November 2011

Flashback #10 – Return Home

The 24 Hour Puzzle Championship took a break last year and will return next month with its 14th edition. I wrote a set for the 12th edition back in 2011. This puzzle is an obscure type in Nikoli called “Oie e kaerou” [お家へ帰ろう] which translates to something like “returning home”. I named it “Return home” in the actual set.

This was one of the last types to be added in my set that year. I remember having too many number placement puzzles and was struggling to find a different genre that has to be interesting and easy to grasp. I was solving Nikoli’s Puzzle Box and luckily found this type. I made two puzzles: one with “24” and one with “HPC”.
[Edit: 11/02/14 – New image for puzzle 1]
[Edit: 23/07/20 – New image for puzzle 2 – thanks to Stefan Liew for pointing out a missing clue]

Return Home – Draw arrows from letters to represent a path that it takes. Paths may not intersect each other. In the end each outlined region may contain only one type of letter. All cells must be used by the arrows.



Puzzle 1: Nov 2011 / Budapest

Puzzle 1: Nov 2011 / Budapest

Puzzle 2: Nov 2011 / Budapest


Light Read #2 – Not numbers? No thanks!

My first Light Read about Nurikabe notations was written during the early days of this blog. I have a lot of potential topics jotted down for future Light Reads that I hope to get across soon. Yes. I still dot the oceans and shade in islands when solving Nurikabe.

Irodoku was an attempt to introduce colours into Sudoku.
This is not the first time someone tried being creative and announce their “Colour Sudoku!!”



This is basically an Arrow Sudoku gone crazy. You have several number banks (red, yellow and blue) and adding any two sums would result in one of three totals (purple, green and orange).
This was the 7th puzzle competitors had to solve in Colour Restore.

The idea is mine as far as I know, but the name isn’t. I was involved in an interview with the chairman of the Thailand Memory Association who said, when he knew I play puzzles; that he was thinking about publishing a Sudoku book. He would replace the 9 numbers with 9 colours and provide 9 coloured-pencils with each purchase.

Seizures, anyone?

Seizures, anyone?

“Wow, what another impractical idea”, was my instant first thought. Replacing Sudoku numbers with anything* is just inconvenient. It may look creative and interesting, but really, its not.

Nikoli's Big Book of Visual Sudoku

Nikoli’s Big Book of Visual Sudoku

The Big Book of Visual Sudoku illustrates the insanity of this already, come on Nikoli you can do much better than this. The glitch is that replacing numbers with letters, symbols or Dora the Explorer immediately chucks any hope of notation out the window.

Did you see the naked pair with Dora and Boots?

Did you see the naked pair with Dora and Boots?

I’ve seen one book use real life pictures of 9 different babies, imagine how would one even fill out the answers? Books like this are malignant tumours of puzzles. They are simply wasting trees and bookshelf space.

Back to the interview, the chairman said he would name his book, “Irodoku”. Iro being Japanese for ‘colour’. Well, not only I was evil enough to pretend to be interested, I even stole his puzzle’s name. Thank you. Up to this day, I haven’t seen Irodoku hitting the shelves yet.

Imagine solving this on paper

Imagine having to solve this on paper

By the way, here’s the answer to Irodoku which can be obtained by maximizing and minimizing a couple of colour banks.


*By anything, I mean anything that doesn’t interfere with the rules of classic Sudoku. I’m not talking about Digital Sudoku or Dice Pip Sudoku where numbers are replaced with fragments of a given clue. That alters the rule of classic Sudoku, and I like those.