Thursday, January 28, 2021

Weather Vanes

Dear reader, I have something colorful for you today. As 2021 is not starting under the best auspices for a lot of people, this will hopefully lighten the mood for some of you. It should also be a somewhat easier puzzle than the previous ones. Enjoy!

You can solve this puzzle online using the F-Puzzles interface: (with colors) (without colors)

Rules :
Each row, column and region must contain the digits from 1 to 9.
Digits in a dotted cage sum to the value in the top-left corner. No digit can repeat within a cage.
Digits on a line must be strictly smaller than one of the two corresponding circled digits, and strictly larger than the other.

#194 Weather Vanes [Killer/Between Sudoku]

Tuesday, January 5, 2021

The Jail

As I said a few weeks ago, Killer Sudoku is ridiculously popular these days, and the trend will probably keep going for a while since there is indeed much to do with the variant. Opportunely, Cracking the Cryptic recently released a new app dedicated to Killer Sudoku ( - also available in other stores) and I have had the pleasure of contributing a large number of puzzles, some of which are available at launch while others will get added to the app in future updates. All the puzzles therein are handcrafted and several other talented authors have contributed, so I encourage you to check it out.

You may rightly feel a bit uneasy at the thought that there are so many killers on the loose... But fear not, they will not stay free much longer. Actually, some of them have already been caught and locked up in a high-security prison, an overview of which I provide thereafter. Now that I think of it, let's hope nobody uses this classified document to plan an escape...

You can solve this puzzle online using the F-Puzzles interface:

Rules :
Each row, column and region must contain the digits from 1 to 9.
Digits in a dotted cage sum to the value in the top-left corner. No digit can repeat within a cage.
A digit in a shaded cell must be greater than all the digits in adjacent unshaded cells.

#193 The Jail [Killer/Fortress Sudoku]

Tuesday, December 22, 2020


Hello, dear sudoku enthusiast. The 81 Cells Youtube channel just hit two tiny milestones (200 subscribers as well as 500 views for the first video released), the perfect excuse to provide you with a themed puzzle. The difficulty of this one doesn't compare to the previous two, but it is not a freebie either - I hope you have a bit of practice on Thermo Sudoku. Enjoy!

You can solve it online using the F-Puzzles interface:

Rules :
Each row, column and region must contain the digits from 1 to 9.
Thermometers are drawn in the grid. Digits on a thermometer must increase strictly from the bulb to the other end(s).

#192 Thermo Sudoku

Tuesday, December 8, 2020

Even more Killer Sudoku

Killer Sudoku's popularity seems to be at an all-time high thanks to Cracking the Cryptic studying dozens of such puzzles - though many of the ones featured on their channel make use of one or more additional constraints. This here puzzle is just another regular Killer Sudoku. Note that it has only 11 cages, which is not the minimum possible but still a rather low number; I have been making a few such puzzles lately. It is also pretty hard and a few years ago I would probably not have published it here, but since there is an evergrowing public for this kind of puzzles, I feel comfortable sharing it. It is definitely not a masterpiece, but there are a few interesting deductions to make along the way. Enjoy!

You can solve it online using the F-Puzzles interface:

Rules :
Each row, column and region must contain the digits from 1 to 9.
The value on the top-left corner of a dotted cage is equal to the sum of its digits. No digit can repeat within a cage.

#191 Killer Sudoku

Monday, October 19, 2020

Still Alive

Would you believe it? It has been more than four years since last I shared a puzzle here. Not that I stopped making puzzles, mind you - I have been contributing to sudoku magazines, competitions and more - but circumstances forced me to take a break with puzzlemaking during the fall of 2016, and I simply never found the motivation to resume my activity with the blog. My life was hectic back then - it still is - and forcing myself to make puzzles every week could not fit in it, and still cannot. For nearly four years I focused on making a living out of selling puzzles (with limited success), and it is only recently that I felt ready to try something new.

Following the postponement of the World Sudoku Championship 2020 and encouraged by the success of the now world-famous Youtube channel Cracking the Cryptic, I recently tried my hand at making sudoku videos with a focus on speedsolving, since there were almost no such videos available anywhere and I felt like I could fill this gap efficiently. I currently release between one and two videos a week on the Youtube channel 81 Cells, and at the moment this is the best place to follow me. I also do livestreams occasionally, on Twitch rather than Youtube since the Twitch interface is infinitely more friendly for this purpose. The Youtube channel is where you want to go to watch spectacular solves of spectacular puzzles, while Twitch streams are meant to be a bit more casual and informative - at least they should be once I manage to grow a bit of an audience... and to fix some unfortunate issues with my Internet access.

Seeing how my previous attempt at sharing sudoku-related content once a week ended, I cannot say for how long I am going to keep this going; but I feel like this is as good a time as any to try. Of course the core of my professional activity remains puzzlemaking, but hopefully this will help me find a balance between the crafting and solving halves of my passion for sudoku.

I have not planned to resume publishing puzzles here on a regular basis, but I might share one once in a while. I am going to publish one right now, at the very least. Be warned: though a most common variant, it is rather on the tricky side of the difficulty scale! It comes in two versions, the original one and, purely for the sake of it, a second one that is more visual. Pick the one you prefer. Here are two links to solve the puzzle online using the F-Puzzles interface designed by Eric Fox: ("minimal" version) ("elephant" version)

Finally, here is a link to Simon Anthony's solve of the puzzle on Cracking the Cryptic:

Rules :
Each row, column and region must contain the digits from 1 to 9.
The value on the top-left corner of a dotted cage is equal to the sum of its digits. No digit can repeat within a cage.

#190 Killer Sudoku

Monday, October 31, 2016

11e Championnats du Monde de Sudoku et 25e Championnats du Monde de Jeux de Logique

À l'adresse des personnes peu familières de la langue anglaise, un compte-rendu en français agrémenté de nombreuses photos est disponible sur le site

Le site étant en cours de construction, il est possible que l'adresse change au cours des prochaines semaines ; je remplacerai bien sûr le lien si tel est le cas. Bonne lecture !

Thursday, October 27, 2016

11th World Sudoku Championship and 25th World Puzzle Championship - Part 2

Then came the puzzles. There is not much to say here, at least regarding my performance; since I did not want to risk making my injury worse, and as I barely had the time to read the instruction booklet before the competition, my intention was to play even more casually than I usually do - and yes, as it turned out, it was possible. Contrary to sudoku, I could not solely focus on the hardest puzzles since there were many of them I would probably never have been able to solve. I picked puzzles somewhat randomly, made tons of mistakes despite my slow pace, and ended up with what was (I guess) my worst result at a WPC, but that was to be expected.
On the other hand, the team rounds went just fine; of course we did not do anything great in terms of score but we all had a really good time. I even got an occasion to shine with my one-man solving of the Double Block in round 16... on which we brilliantly managed to swap two "3" stickers, awarding us with 0 point.

Regarding the overall results, Endo Ken was first after the preliminary rounds with a solid lead on Ulrich Voigt and Palmer Mebane. And by "solid", I mean that he crushed the competition until this point; it was really impressive. Unfortunately for him the finals can bring their share of surprises, and the very first puzzle (Coded Nurikabe) got him stuck for more than enough time for Ulrich and Palmer to get past him. In the end, it was yet another crowning for Ulrich, followed by Palmer and Ken, with Philipp Weiß as a somewhat unexpected number 4. Congrats to the four of them.
Also, a special mention to our own Olivier Garçonnet who made it to the under 18 play-offs and got himself a bronze medal. Way to go!

Now for a few words about the championships from a broader perspective.


To say things as they are, I am having a hard time finding something that did not go as smoothly as possible. Zuzana Hromcová did a terrific job as the head of the organising team. The army of volunteers were prompt and efficient, marking was done in a very reasonable amount of time and for the first time, online results were available as the competition was going. I know that was appreciated by people who followed the WSPC. Queries were treated efficiently by Peter Hudák and the group of judges and was there some urgent matter to discuss, it was fairly easy finding someone of the organizing team. Also, I should mention that each and every volunteer was not only efficient but friendly and doing their best to help when needed, which is to be saluted. Hats off!


For having solved quite an amount of slovak sudokus and puzzles (although not that many in the past two years), I thought I had a good idea of what to expect, i.e. a good variety of rather easy puzzles, nicely made and with quite a lot of original ideas but rarely striking in design. Well, I was completely caught off guard by what Matúš Demiger and his co-authors had done. I was absolutely not expecting a round such as the "Basics" one, and several sudokus had me surprised by the thought that had gone into making them. They were still mostly on the easy side but, regarding their quality, definitely on par with what had been done the previous years.

Additional thoughts

There were several innovations this year; one of them being that tons of additional awards/prizes were given during the ending ceremonies. There was one for guessing who would end at the 11th in sudoku and 25th place in puzzles, one for the worst writer (won by my teammate Olivier Garçonnet, who looks like he will be a great successor to Timothy Doyle in this category), and many more. All in all, it was funny and made the ceremonies more light-hearted than usual, which I enjoyed.
On the evening, some more events were organized such as a "Pyjama Sudoku Contest" and a Team Competition. I did not take part in many of them unfortunately, since I was trying to get all the rest I could to make my arm better; but the echoes I had were all positive.
Another thing the slovak team added was team play-offs. Well that was, in my opinion, the best part of the competition. It was really, really good and from a player perspective I dearly wish we will see some more of these. The puzzles were nice, the difficulty was spot-on, and there was just enough tactical planning involved to make things exciting while still consecrating the best sudoku-solving team. Also, it was much less stressful than the individual play-offs where you know you have only yourself to rely on and cannot afford a single mistake. I am glad I stayed in the A-team so that I could take part in this.

I could go along but that's enough typing for today. I will complete this or post another message if I find some more matter to discuss tomorrow.

If not, see you next year in India!