The Art of Puzzles

Friday Puzzle #152 - BIST-inspired Irregular Sudoku

Fri, 25 May 2012 07:01:25 GMT

Some say imitation is the sincerest form of flattery. This puzzle resulted as I was playing around the construction space of one of my favorite puzzles from the BIST which used the same cage and sixteen given pattern. Here the first few digits go in the same, but I added my own calling card after that and the remainder of the puzzle solves pretty differently and is harder than the version we saw. I hope you enjoy this Irregular Sudoku which I wrote from China before the playoffs.

Rules: Place a digit from one to nine into each cell so that no digit repeats in any row, column, or bold region.

Final BIST Update

Fri, 25 May 2012 03:02:53 GMT

A funny thing happened after winning my third world sudoku championship in Hungary last year. I didn't get one interview. Not a single reporter on site. Not a single email or phone query when I got back home. So for those wondering why I never linked to any new video of me being quirky after my most dominant sudoku tournament win against the strongest field yet, that is why.

Well, I expected BIST 2012 to be much different. With the Beijing Media Network being a primary sponsor, it was obvious interviews would happen. Two cameras got me at the airport as I exited customs. More got me on the daily excursion. I got pulled out of my hotel room while relaxing pre-opening ceremony for an interview. Then there was a press conference run during the start of dinner where six solvers (the top four from last year who would again qualify as the top four this year and two Chinese solvers) were asked questions. When the instruction meeting later was over they wanted video of me offering tips to the youngest Chinese competitor, and shots of me solving puzzles. During the competition, it felt like all the 10 minute breaks became five, because I certainly had to share the world an update on that last round. And when I wanted to go hide after one of my worst playoff performances in memory, I instead stayed and grinned and gave another closing set of answers talking about how beautiful the puzzles were, to highlight Chen Cen's (and others?) work to make a great tournament. Given how poorly I performed, I bet almost none of this footage was used. Still, there are often open shot rolls given out as B-reel footage for other agencies that might run a story. I found such footage (I'm most of the last 90 seconds) that comes close to a BINGO on the Snyder Sudoku footage game card, what with excessive hand motions, awkward shots of me looking at nothing in particular, the "you know" problem, the stuttering, and my favorite, an odd but edgy quote - here it is equating sudoku with other addictive drugs (cleaned of above problems):

"If you're having a stressful day you can take a 10 minute break and go do a puzzle. Some people may use something else for their relaxation: smoke a cigarette, get a drink, .... I solve a puzzle. So, maybe I'm a strange person in that way but it is relaxing and fun."

I find myself pretty funny when I'm jet-lagged and trying to make sudoku sound interesting. Maybe you will too.

ETA: Here is one of the better print pieces - at least in that it highlights some of the puzzles as I was trying to do (this is from after the semi-final): "Most Sudoku puzzles are designed by computers, which are not really interesting... if you make poetry by computer, it would not be interesting poetry either. But these have very artistic, logical themes."

Another BIST update

Sun, 20 May 2012 04:32:50 GMT

Around 2007, when I first saw Blackout Sudoku in GAMES magazine, I must have channeled my inner Roger Ebert when my reaction was "I hated, hated, hated this variation". I've never sought them out to solve because they are not fun and I like to enjoy puzzles from time to time. It runs too counter to normal thinking, and is far too easy to make a mistake when you are actually, you know, trying to solve with sudoku approaches.

Five years later, after botching the Blackout in a competition round with >15 minutes of time to do just it, I managed to also botch the Blackout in the semi-finals with >15 minutes of time to do just it. Not a good year for me. With that puzzle worth slightly more points than others people stumbled on, I fell to near the bottom of the all but one done group. Add that to forgetting to pack pencil leads, and not reading the instructions before arriving here which would have led me to bring highlighters for the Windmill Sudoku, and it is clear to me that my focus on work and puzzle construction is really affecting my puzzle competition as I simply have no time or energy to do the right preparation.

Jan had probably the best semi-final performance by many minutes. Even if I'd cleanly gotten the Blackout done in the first of three tries, I would have been behind by 3 minutes. Unfortunately, he transposed digits in one of the puzzles and lost all time bonus and 3 positions to fall to 4th. Instead, the finalists are Jakub Ondrousek and Kota Morinishi. I wish them luck in the finals starting in a couple hours.

ETA: And Kota takes the title in about 24 minutes of solving (and 6 minutes of grading). The two competitors were tied after the first puzzle but Kota did good work on the second classic sudoku (seeing a column 4 deduction rapidly from spotting what I'd call a nontrivial hidden pair) and built a large lead on Jakub. Even when Kota slightly stumbled and needed to restart the fifth Diagonal puzzle, Kota was still about 2-3 minutes ahead. His solving style was very interesting to watch (I'd only seen it briefly while he was finishing in Eger last fall) and his manual dexterity at writing numbers is far better than mine. Congratulations to the new champion.

Brief BIST Update

Sat, 19 May 2012 12:16:48 GMT

The puzzles are again tremendous; my performance, not so much. When you submit a sprint round early but forget to look at the puzzle on the first page, you are certainly making boneheaded errors. Repeat this sort of thing all day with at least one broken puzzle in each round and you get the kind of average performance I've been having. Fortunately, my average is still good for ~4th, and I will have a shot tomorrow in the Semifinals. Jakub, Jan, and Kota round out the top group, all the usual suspects, with Hideaki, Tiit, Florian, and Yuhei sitting another 10% back in 5th through 8th. It will be a dramatic race tomorrow I am sure.

Friday Puzzle #151 - UK Thermo Sudoku

Fri, 18 May 2012 07:01:09 GMT

As this entry is posting, I'm in China at the 2012 Beijing International Sudoku Tournament. I'm hoping to have another fun trip, even though none of my US, Canadian, UK, or Indian puzzle friends will be at the tournament this year making for much less interesting meal conversation. To be completely honest, my tournament expectations aren't too high. Since I won my third world championship six months ago and started my new job, I haven't had too much time to "train" at sudoku and my LMI sudoku test performances have been really slipping. Being out of practice means losing "sprint" speed mostly, and last year's playoffs were entirely sprint puzzles. So my hope is to finish as good as last year at the BIST (4th or better), but I think I only have an outside shot of winning. Jan, Jakub, Tiit, and Kota (if not others) all probably have a better chance than me at the moment. Best of luck and skill to all the competitors.

I wrote some sudoku for the recent UK Open Sudoku Championship and this week's entry is another one of them. Enjoy!

Rules: Place a digit from one to nine into each cell so that no digit repeats in any row, column, or bold 3x3 box. In addition, the digits in each "thermometer"-shaped region must be strictly increasing along any marked path from the circular bulb to an end.

Friday Puzzle #150 - UK Arrow Sudoku

Fri, 11 May 2012 07:01:24 GMT

I wrote some sudoku for the recent UK Open Sudoku Championship and this week's entry is one of them. Enjoy!

Rules: Enter a digit from 1 to 9 into each cell so that no digit repeats in any row, column, or 3x3 region. Digits in the circled cells represent the sum of the digits along the path that each arrow travels. Digits can repeat within an arrow sum, provided this does not violate the standard sudoku rules.

Friday Puzzle #149 - Star Battle

Fri, 04 May 2012 07:02:12 GMT

After a string of sudoku puzzles, here is something slightly different.

Rules: Place stars into some cells in the grid so that each row, column, and region contains exactly two stars. Stars cannot be placed in adjacent cells, not even diagonally. (The example uses just one star.)

Example:

Puzzle:

Friday Puzzle #148 - Nonconsecutive Sudoku

Fri, 27 Apr 2012 07:01:01 GMT

While this might look like another interesting classic sudoku from my new book "The Art of Sudoku", you'll have a lot more success treating it as the nonconsecutive sudoku that it is. Enjoy.

Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region. Consecutive digits (ie 3 and 4) cannot appear in any pair of horizontally or vertically adjacent cells.

Friday Puzzle #147 - The Art Of Sudoku Sampler

Fri, 20 Apr 2012 07:12:02 GMT

While I thought it might take a couple weeks to get listed online, I found that my latest book The Art Of Sudoku is already available for order. Feel free to get it at Barnes and Noble or at Amazon.com. I should be listed in UK, European and Australian sites soon too.

This week's Friday Puzzle will complete a 6-puzzle sampler I had in mind for this work (here is a pdf of the whole set laid out as in the book). The 6 puzzles span a range of difficulties and showcase very different kinds of themes I used in the book, including patterns in the digits, themes using the properties of the numbers like even/odd, large/small, or increasing/decreasing series, geometric patterns, and logical themes. Today's puzzles, #45 and #60, showcase some unusual given patterns that lead to good average difficulty puzzles.

Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region.

#45

#60

That New Book Smell...

Thu, 19 Apr 2012 01:59:33 GMT

Until a book is available for sale, it is hard to celebrate the work that went into it. But I find there are always tantalizing moments of excitement as the finished product starts to come together.

Last week, for example, I got to see the cover artwork of a book I spent most of early 2011 working on with Mike Selinker, making this work feel much more real than it used to. The cover is still not public, even if the book's identity and possible (but not probable) release date is listed now. Another book, which is either about sudoku or goldfish, is advancing now too.

Well, today I discovered the "new book smell" is just as exciting when you are the publisher. I've been working on this classic sudoku book since January 2012, so the battle of creativity is much fresher in my mind. I finally submitted my files to the printer over the weekend. It will take a little time to show up for sale online at usual places like Amazon and B&N, but I can now say for certain that you too can be holding The Art of Sudoku in May. Until then, I can only tease you with this image of the (pretentious?) author/publisher and the first copy of his work. The book is hiding my smile!

Friday Puzzle #146 - Thermo-Sudoku

Fri, 13 Apr 2012 07:01:46 GMT

Rules: Place a digit from one to nine into each cell so that no digit repeats in any row, column, or bold 3x3 box. In addition, the digits in each "thermometer"-shaped region must be strictly increasing along the path from the circular bulb to the end.

Friday Puzzle #145 - 04/06/12 TomTom

Fri, 06 Apr 2012 07:04:11 GMT

Some dates deserve a certain kind of puzzle. These three numbers seemed to offer a good combination for a TomTom puzzle. Enjoy!

Rules:
Place a single digit from 1 through 6 into each empty cell of the grid so that each digit appears exactly once in each of the rows and columns. The value in the upper-left of each bold region indicates the result after some mathematical operation (addition, subtraction, multiplication, or division) is applied to the numbers in that region. For division and subtraction, start from the largest number. Numbers can repeat in a region provided they do not repeat in any row or column.

Friday Puzzle #144 - Make Room for Pentapa

Fri, 30 Mar 2012 07:05:24 GMT

I was chatting recently with someone about the feasibility of extending LITS to pentominoes. That seed of an idea matched with my existing Make Room for Tapa style for this week's Friday Puzzle.

Rules: Place the 11 given pentominoes into the grid, exactly one per region with rotation/reflection allowed, to form a valid Tapa.

In a valid Tapa, all shaded cells must be connected, but no 2x2 square may be entirely shaded. Numbers in a cell indicate the length of shaded cell blocks in the neighboring cells. If there is more than one number in a cell, there must be at least one unused cell between the black cell blocks. There are no tapa segments on the cells containing numbers.

Friday Puzzle #143 - The Art of Sudoku - Examples #3 and #4

Fri, 23 Mar 2012 07:31:09 GMT

Since my posting of two weeks ago, I've now retested all of the 120 puzzles in the book and settled on a final order. They are roughly sorted by difficulty, but this is somewhat subjective and I often tried to separate puzzles with particular features that might feel similar if done back to back. For reference, you have seen #30 and #108 in past weeks.

I'm not going to release too many more before-hand (6 out of 120 is probably my maximum), but to capture the missing quarters of the book, here are puzzles #3 (easy) and #86 (moderately hard) which use two different interpretations of a similar genre of visual theme. Enjoy!

Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region.

TAoS #3

TAoS #86

Friday Puzzle #142 - Make Room for Tapa (DD Part 5)

Fri, 16 Mar 2012 15:42:02 GMT

I'd originally planned to post this, the original (and harder) Make Room for Tapa puzzle from the Double Decathlon, around the time of a TVC contest where I could advertise it as a fun activity for the weekend. Oddly, this instruction booklet doesn't give me as much confidence of a fun activity for the weekend. There is an optimizer hiding as a puzzle -- one of the things I hate most in competitions. There are puzzles putatively about science, but Balance Tapa ignores torque and is hardly in balance, and Meiosis Tapa seems to take Meiosis (division without replication) and adds in Mitosis, Cancer, Breaking the Law of Conservation of Matter, and all other sorts of wacky things. Puzzles that destroy or alter clues are, after hidden optimizers, amongst my least favorite puzzles. This test has several of those styles. All I can say is I expect it to be very tough for me, and so maybe it actually is fitting then to post the "too hard" form of my original DD Tapa, after a warm-up Easy one.

Rules:
Shade some cells black to form a continuous wall. There cannot be a 2x2 square of cells that are all shaded. Numbers in cells indicate the length of connected black cell groups in the neighboring cells; if there is more than one number in a cell, then there must be at least one white cell between each of the indicated black cell groups. Cells with numbers cannot be a part of the wall. The grid is also divided into regions by bold lines; exactly five cells must be shaded black in each region.

Example and Solution:

Easy:

Hard:

The easy puzzle was a design to get an almost symmetric presentation of 2's, but with the different theme elements in the upper-left and upper-right corners. The 2222 square in 4 cells hit me during a run as a cool two-state opening, and the solution grows out of that corner using region shapes maximally.

The hard puzzle, with symmetric regions and clues, used a really big constraint to get going. Namely, the Tapa must cross the center. In this, the original form, solvers must realize the UL and LR corner cannot be connections, which means the big middle is crossed by the Tapa somewhere. And with 4 of the 5 cells accounted for by other clues, there is only one area it can be crossed but it is hardly easy to figure out where. The amendment to the puzzles made the UL and LR blocks much easier, and let some instant blacks get in too. It shaved the right 2-5 minutes off of this still challenging puzzle. The test form is here.

Solutions:
Easy
Hard

Friday Puzzle #141 - The Art of Sudoku - Sample #2

Fri, 09 Mar 2012 03:46:44 GMT

This past weekend I finished constructing all the puzzles in my forthcoming classic sudoku book: The Art of Sudoku. I now have a first draft of the book laid out, but still need to check some timings, make cover art, and do other small fixes. But my Spring target will certainly be met. I wanted to share another sample puzzle from this book (see here for Sample #1).

One new trick I've been using recently in constructing is something I learned from creating Just One Cell Sudoku. Basically, the steps you take to hide a very clean logical deduction that only gives one new cell can be used for a whole puzzle provided you are very careful that no easier moves are possible and can work backwards from that cool state. This week's sample is one of the harder puzzles in the book, but hopefully showcases what a good handcrafted puzzle can feel like at the higher difficulty levels.

Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region.

Friday Puzzle #140 - Big Tent Party (DD Part 4)

Fri, 02 Mar 2012 08:20:09 GMT

Tents is a puzzle type that seems to me to be close to the top tier of classic puzzles (like Battleships, Skyscrapers, and many others) but somehow always comes up a little bit short as it doesn't seem to offer enough interesting, different logic to be as good as other placement puzzles like, say, Minesweeper or Star Battle (other classics). In the last two Decathlon tests I've explored a slight variation that I thought could add more variety to Tents, although possibly with mixed success. Here are the "big tent" puzzles I wrote for the most recent test.

Rules:
Place a tent, covering two adjacent cells, next to each tree so that the tent and tree share one edge. Tents can be oriented in any direction but cannot occupy cells containing other trees. Tents do not touch each other, not even diagonally. The numbers outside the grid indicate the number of cells covered by tents in that row or column.

Example:

Easy:

Hard:

Here, the small puzzle was written to have a clear diagonal theme (and the no diagonal touching rule leads to a zigzag placement in the center). The harder puzzle was written to have a congested center that really has two possible general placements, but where another really cramped zone would be the break-in point. See if you can find which corner has very limited options, to set the center and eventually the rest of the puzzle.

Solutions:
Easy
Hard

Friday Puzzle #139 - SVPF Youth Sudoku

Fri, 24 Feb 2012 07:47:53 GMT

And to close out the 6th Silicon Valley Puzzle Fest puzzles I wrote, here are the three youth sudoku tournament puzzles, which can be enjoyed by solvers of all ages.

Rules: Insert a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or 3x3 box.

Friday Puzzle #138 - SVPF TomTom Puzzles

Fri, 17 Feb 2012 07:21:46 GMT

Here are the TomTom bonus puzzles from the 6th Silicon Valley Puzzle Fest, which was a new bonus round this year to go along with my seminar talk. The youth puzzle is meant to have a little character but mainly to be fairly approachable. The adult puzzle certainly has a really strong theme (and title). Enjoy!

Rules: Insert a single digit from 1 to 8 [1 to 6 in the smaller puzzle] into each cell so that no digit repeats in any row or column. The digits in each small marked group must equal the value of the clue given in the upper-left corner of that group when the indicated operation is applied to all digits in that group. Start with the largest digit for subtraction and division.

Youth:

Adult:

Tapa, Tapa, everywhere... not a moment to think.

Sat, 11 Feb 2012 05:21:30 GMT

This weekend features the start of two Tapa tournaments at LMI, the Classic Tapa Contest which runs for 50 straight days, and the first of this year's four Tapa Variations Contests. Both come highly recommended, although for reasons of not puzzling on weekdays because of the needs of my new job I will be sitting out the CTC because missing 40+% of the puzzles will give me no shot no matter how well I do on the classics. MellowMelon is my pick (not a hard choice) but he'll need to avoid the two minute penalties to pull it off.

The Tapa Variations Contests, on the other hand, are 75 minutes on four different weekends and I'll find time in my schedule for them even when, like this weekend when I'll be out and about all Saturday and Sunday, I only found just enough time for the test (so couldn't even practice on all of Para's pre-puzzles). Last year's scoring rules left cause for some concern, but the puzzles were stellar. With updated scoring rules that fit better within the LMI model (and that match my three recommended fixes from last year), I look forward to a real interesting competition.

Thanks Serkan, and good luck (and skill) to all the competitors.

Friday Puzzle #137 - SVPF Killer Sudoku

Fri, 10 Feb 2012 05:06:46 GMT

Here are two more puzzles from the 6th Silicon Valley Puzzle Fest. In the past there has been a Youth and Adult bonus round in Killer Sudoku and I made an easy and a medium puzzle to serve these roles. Having talked about the lack of value to two-cell 9, 10, and 11 clues in my lecture the day before, I thought the inclusion of so many in the adult puzzle would be kind of neat.

Rules: Insert a single digit from 1 to 9 [1 to 6 in the smaller puzzle] into each cell so that no digit repeats in any row, column, or bold region. The sum of the digits in each small marked group must equal the number in the upper-left corner of that group.

Youth:

Adult:

Friday Puzzle #136 - SVPF Adult Sudoku Tournament Puzzles

Fri, 03 Feb 2012 05:03:34 GMT

Last weekend was the 6th Silicon Valley Puzzle Fest. I've provided the sudoku puzzles for the last four years (links to 2, 3, 4, 5). This year I again provided the classic sudoku, and added in puzzles for two bonus rounds. I'll be sharing all of these puzzles over the next several weeks. This week, I'll share the four adult tournament puzzles. A cumulative time of about 15 minutes was needed to make the final, which was won by Jordan Chodorow of LA.

Rules: Insert a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region.

Round 1:

Round 2:

Round 3:

Round Final:

Friday Puzzle #135 - Loop the Loops (DD Part 8)

Fri, 27 Jan 2012 04:53:45 GMT

This weekend marks the last chance to compete in the LMI Puzzle Marathon test. It's a unique contest with 10 separate puzzles you can solve at any time, against their own clock, but with large puzzles that can take dozens of minutes to dozens of hours to solve depending on your skill. One of the puzzles is a type I explored on my Double Decathlon test, so I thought I'd repost those puzzles this week for any who might want the practice. I've discussed strategies for solving this puzzle type before too.

Rules:
Draw a single closed loop that connects neighboring dots horizontally or vertically (but not diagonally). The loop cannot intersect of overlap with itself.

Some numbers appear in the grid as clues; as in a Slitherlink puzzle, a numbered square indicates exactly how many of its four edges are used by the loop.

Some circles (either white or black) also appear in the grid as clues; as in a Masyu puzzle, the loop must pass through all of these circles. When passing through a black circle, the path must make a 90 degree turn and extend at least two dots in both directions. When passing through a white circle, the path must go straight and must turn at at least one of the adjacent dots.

Example Solution:

Easy:

Hard:

When merging two styles with different design rules (Slitherlink is always symmetric, Masyu is rarely symmetric), it is hard to know exactly what the hybrids should look like. I took two rather different approaches with the puzzles here.

The first "Easy" puzzle is fully symmetric. Moreover, when looking at clue identity, it is fully anti-symmetric. All white circles have a rotationally opposite black circle. And every 0,1,2,3 slitherlink clue has a rotationally opposite 3,2,1,0 clue. I almost got a nice diagonal pattern with the numbers but had to move one pair of givens at the end (you'll know which ones) to get the final puzzle to work just right. Still, after making this puzzle, I find the presence of different styles of clues makes the symmetry much harder to pick out than in a normal Masyu or Slitherlink alone, but perhaps this particular pattern of circles and numbers is part of the problem.

The second "Hard" puzzle throws symmetry considerations out the window, and instead takes a quadrant theme to some interesting places. Each quadrant has only one kind of Slitherlink clue, and even numbers share space with white circles and odd numbers with black circles. I chose this arrangement as a lot of the interesting effects of black circles in a slitherlink hybrid are with odd numbers, where the white circle effects are more subtle but definitely lead to a challenging lower-left corner. This puzzle also uses some "loop" constraints, such as free end counting, near the finish, which made the puzzle the right difficulty for the test. I hope you enjoy both of these, and agree with me that more Loop the Loops would be nice to see.

Solutions:
Easy
Hard

Friday Puzzle #134 - The Art of Sudoku - Sample #1

Sun, 22 Jan 2012 18:09:40 GMT

I'm hard at work putting together my first book of classic sudoku, which will also be my first self-published title through Grandmaster Puzzles. While it is easy to view this as just a test of my publishing pipeline since classic sudoku are easy puzzles to mass-produce, I've actually been spending the time to make absolutely beautiful and elegant puzzles. Here is the first teaser puzzle from the book which should be out this spring. It's also a good warm-up puzzle for those competing at the Silicon Valley Puzzle Fest next weekend.

Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or bold 3x3 region.

Upcoming Puzzle Tournaments

Fri, 20 Jan 2012 17:34:56 GMT

Next weekend is the 6th Silicon Valley Puzzle Fest at the Morgan Hill Library. On Saturday is a day of puzzle-related talks, including a session on TomTom Puzzles from me at 11:25 AM. On Sunday are two tournaments - one for crosswords and one for sudoku - and I will be contributing the sudoku puzzles to this tournament. I will also be providing bonus puzzles for a Killer Sudoku round, and for a TomTom round. Whether you can only make the discussions or only make the tournaments, it is a fun weekend of puzzling and I hope you can come out.

For those far away from the Bay Area, Sudokucup 7 will be held online next weekend; while I will be unable to compete, I encourage you to. I wrote the puzzles for the third Sudokucup, and I view Kodyn's tests as one of the starting points for the booming online competition scene, so I look forward to seeing what he has put together this year.

PS - A Friday* Puzzle will be coming later this weekend, and I think the asterisk will become a permanent thing for a little while.