The last time we fielded at least one full team to the World Sudoku Championship was in 2017 (Bengaluru). Last year, we had a lone representative who joined the Toronto WSC. So when we learned it would be held in China this year, some of us decided to join while it was relatively not too far away.
The 2024 World Sudoku and Puzzle Championships (WSPC) were held in the Pinggu District of Beijing. We stayed at the Jinhai Lake Grand Metropark Hotel. The temperature tended to hover around 15-20°C, a pleasant change from the hot and humid tropical weather we have at home. The 17th WSC itself was held at a convention center next door.
The hotel grounds contain several buildings surrounding a garden and pond.
Cebu doesn't have a direct flight to Beijing, so two of us flew out at 2 AM for Shanghai, where we met up with the Manila-based half of the team before proceeding to Beijing. We got to the hotel a little past 4:30 PM, where we met the sixth member of our team and got a complete team picture in the hotel lobby.
Some members of the team had never met in person before this event. Photo by Matthew.
Because we haven't joined many international events, one memorable part of this was seeing / talking to some of the people whose names we only read about online. This was my first time meeting Kishore Kumar of India, who has done video solves of some my puzzles on Unshackling Sudokus and Puzzles. Right before we left for the airport, as we were sitting in the lobby, I got to talk with Dutch team captain Richard Stolk, who resumed his Sudoku Variants Series after WSPC.
A cultural presentation from some Chinese students at the opening ceremony.
I had wanted to think a bit about Round 13 before calling it a day. But after over 24 hours without proper sleep, even writing notes on the printed Instruction Booklet was tiring, and I chose to just get some rest instead.
WSC - Day 1 AM
Then I woke up at 5:15 AM and could not go back to sleep. The excitement was real.
When I joined the Asian Sudoku Championship last January, I didn't think of taking pictures of each team member at their desk before the contest begins. This time, I got pictures of my 5 teammates, then promptly forgot I needed one too. Just before the final team round on Day 2, I got one, and we still have a complete set of individual pictures.
C̶l̶o̶c̶k̶ ̶F̶a̶c̶e̶s̶ ̶S̶u̶d̶o̶k̶u̶,̶ ̶w̶h̶i̶t̶e̶ ̶c̶i̶r̶c̶l̶e Clockwise from top-left: Candice Solidarios, High Tan, Matthew Co, Desiree Go, Sed Holaysan, Fred Gutierrez
I let my teammates have their pick of the four assigned Philippine-A seats. Fred, who speaks some Japanese, took the seat next to Japan's Rintaro Matsumoto, who ranked 15th in his WSC debut. High picked a seat near the front, next to a solver from Poland, and Candice got a seat next to one of the Koreans. This left me a seat next to Annick Weyzig from the Netherlands, a familiar name from online competitions. Since my seat was near the center of the hall, it became our default place to gather between rounds. If you've been to sudoku competitions, you know why we gather - it's to talk about which puzzles we solved...or failed to solve. Misery loves company, after all.
Seating arrangement. The 84 official team A players are seated in the front half of the hall, while team B players and IO (individual participants) are in the back half.
Minutes before the first round began, Tom Collyer (UK), who was seated at the table in front of me, asked a passing Tiit Vunk if he had any tips. The two-time world champion from Estonia thought for a second, then commented matter-of-factly, "Don't make mistakes". This was very good advice, but unfortunately I did not follow it.
Round 1: The first round was themed on the handscroll painting Along the River During the Qingming Festival. I imagine each design is based on something in the painting, as I've seen the boat, camel, rainbow bridge, and gate tower, but I'm not sharp-eyed enough to find the rest. I went for the Parity Lines for 45 points, the Pencilmark for 90 points, and then the Consecutive On Line for 65 points (I was quite excited about this one, as it's one of my favorite variants for drawing things). I then attempted the Clone, broke it, and with 2 minutes left, decided to just take out the Abacus (5). Once time was called, I added up what I thought I had solved and was hoping for 205/400.
It was only after dinner that I found out what a disaster this round had been. I got Parity Lines and Pencilmark very wrong, and the Consecutive On Line had an 8 instead of a 7 in one cell. So I got 5/400. Welcome to WSC.
A miserable start. This is what you get when you don't listen to a world champion's advice.
Round 2: An easy classics round, 8 grids in 15 minutes. Getting stuck on Classic 4 was frustrating given the short time limit. I was hoping for 90/150 here, but one of my 20-pointers was wrong and I ended with 70/150.
Round 3: I started with the Consecutive (30), then slowly worked out the Antiknight (50). I attempted the 40-point Argyle for two minutes, didn't make much progress, and solved the 3D Sudoku (75) instead. With my last 10 minutes I decided that going for a 60-pointer seemed risky and I decided to go for the Extra Region (30), then the Renban (30). This was the only round where I got at least 50% of the base points, with 215/400.
Round 4: This round was all hybrids of 2 rulesets. I was not looking forward to this, especially when there was nothing under 40 points.
One memorable question from the Q&A session the night before was when someone asked, "Will the geometry of the competition puzzle for Penta Diagonal Sudoku be the same as the example in the Instruction Booklet?"
The ominous answer was: "You will find out when you see the competition puzzle."
I skipped it, even when the competition puzzle turned out to have the same geometry.
Penta Diagonal Sudoku in the Instruction Booklet. Note that IB puzzles are not necessarily representative of the actual puzzle difficulty.
I started with the Pointing Arrow (40) just to get going, then got the Superconsecutive Extra Region (60). Then I went for the 75-point No Touch Windoku, where I got stuck, bifurcated, ran into a contradiction on both ends, and gave up. At this point I had about 12 minutes left and my score was 100/500, so I tried the 50-point 3D Consecutive. After a couple of minutes without getting the break-in, I illogically flipped over to the Star Battle Passage (80), made more than one random guess, and filled the grid in the nick of time. Somehow it was right, and I scored 180/500.
WSC - Day 1 PM
Another memorable question from the Q&A session was, "Will all the possibilities for 24-Trio Sudoku be given?"
The answer was: "No, you have to do it yourself. We wrote a Python program for it."
The example puzzle for 24-Trio Sudoku in the Instruction Booklet.
As we stood around the competition hall, talking about the upcoming Round 5. High proudly showed us his list of possibilities for the 24-Trio Sudoku. I commented dryly that I was just going to skip that variant, which elicited laughs from the table behind us as Tyler Chen and Thomas Luo of the USA team showed us their own list. It did not encourage me to reconsider.
Round 5: I got the 30-point Killer Sudoku quickly enough, then managed to break the 35-point Upper Right Heavy Killer twice before getting it to work. I then moved to the 80-point monster of the round, Positional X-Sums. I broke it twice as well and burned far too much time before getting it right. I attempted Multiples in the last few minutes but couldn't finish it. So I ended with 145/400, regretting that I never had time to try the other well-known variants like Arrow, Ratio, and Little Killer. I've done the 24-Trio by now, and do not regret skipping it.
Round 6: 15 minutes for two linked Irregular Sudoku grids with the same solution. I did not understand this puzzle during the contest, but some people submitted in under 10 minutes. Meanwhile, I had four correct numbers in the grid for 8/150. After we got home, Fred figured this one out and pointed out the key step I had missed.
Round 7: This was an Uncertainty/Liars round. I started with the Outside Sequence and just completely missed the easy break-in, skipping it after a couple of minutes. A cursory look at Greater-or-Sum told me the center box and a few other cells could be filled, so I tried it, then got stuck, even after a bifurcation. At this point I was sitting on 0 points with a third of the time gone, so I decided to forgo the high-pointers, and picked up Unmarked Thermo (30), Arrow-or-Thermo (40 with a nice Yin-Yang pattern), Yin-Yang (50), and Local XV (55), for a total of 175/450.
Round 8: This was the first team round I've ever played with a Philippine team, so I was quite excited. A hopscotch grid with 10 spaces was given, where each space contained 2 or 3 sudoku grids to be solved. Each of us would throw a sandbag, and whichever space it landed on would determine which sudoku that person had to solve.
Each puzzle had to be solved individually, and each person could not get another puzzle without submitting (or giving up on) the current puzzle. So this was mainly a matter of assigning who wants to take on which puzzle, and hoping that your sandbag doesn't bounce into a puzzle you hate. The list of puzzles for each space was only given out the night before, so we made a quick split of them, and I ended up going for the math puzzles. Between 1 and 9 (40 points) felt easier than I expected, but I took longer on the Arrow (30). I made a couple of localized mistakes on the Mathdoku (75) but fixed it in the end. I attempted Irregular Dots (60) in my last few minutes, but couldn't get it in time. We got 500/1200.
Round 9: A large Sudo-kurve on an A1 paper. It's actually fun to work together on a large linked puzzle, but the problem is that one mistake can snowball if it's not caught quickly. We caught some mistakes early, but another slipped past us. In the last minute, we were running around trying to fix what we could, and this turned out to be our best team round with 1050/1200.
It's a good thing this photo was taken at the start of the round, while we still looked calm. Photo from the organizers.
After doing 9 rounds of sudoku during the day, evenings are for rest. Well, not really, they're for doing more sudoku. There was a side tournament and we could watch the finals of the Sudoku Grand Prix. However, we had no idea how to approach Round 13, and honor demanded that we at least try to figure it out. So with heavy hearts, we skipped the side tournament and the GP finals to do a bit of planning.
After a lot of shufffling strips of paper, we hoped to get a nonzero score for R13. Despite how it may look, we did not coordinate to wear blue. Photo by Fred.
WSC - Day 2
Round 10: Difficult classics. After struggling on "easy" classics in Round 2, I was not too hopeful about this round. I did both 25-pointers and all three 30-pointers, plus the 35-point puzzle, but one of the 30s had a one-cell error and I ended with 145/300, just short of 50%.
Round 11: Compared to a typical Sudoku Grand Prix round, this had:
- 0 classics instead of 4-6. Great for me, because I rarely do classics on the GP anyway.
- 18 variants instead of 8-10. Still great for me, since lets me ignore the variants I don't like.
- 100 minutes instead of 90. Do I even have to explain why this is great for me?
So I was quite optimistic about having fun on this round. You may or may not agree with my opinion.
In the GP, I have a habit of just going straight for the highest pointer of the round, which often backfires spectacularly. This time, I decided to be a bit more cautious...meaning that I would do one low-pointer first.
So I went for the Pyramid (30), got stuck and gave up in the first 5 minutes. Then I reverted to my usual GP ways, went for the 95-point Numbered Rooms and solved it. Go figure. I stared blankly at the 70-point Cloned Inequality for 2 minutes without finding the break-in, so I skipped it. I solved Disjoint Groups (55), Expanded (35), Rossini (50), Even Sandwich (70), and Brick Wall (65). I attempted the Incomplete Quadruple (75) but broke it and didn't feel like I understood the puzzle enough to redo it. At this point I switched over to low-pointers, picking up Kropki (30), Citywalk (40) and Outside (40). I went back to the Pyramid with my last few minutes and still didn't figure it out. I have no idea what I missed during the contest, as it solved easily enough afterwards. None of my submissions had unexpected errors, and I got 480/1000.
Round 12: A team round with four mutually exclusive grids - cells in the same relative position across the four grids do not have the same number. (For example, if R1C1 = 3 in one grid, then R1C1 in all other three grids cannot have 3.) This sounded simple in theory, but having to glance back and forth between your grid and three others is not that easy.
High cleared most of the Killer quickly, but then progress was slow after that. Towards the end of the round, I thought I had solved the Irregular (after a lot of looking back and forth), and we hoped that the completed Irregular (300 points) and the partial answers on the other grids would net us at least 600 points. The only problem was that I had eight cells swapped around on the irregular, which turned it into an instant zero. We ended with just 333/1200 points for this round.
Round 13: And finally it was time for the round we'd spent the previous night preparing for. In this round, we would be given 36 columns (stickers) for 4 sudoku variants, and we had to assemble the grids of the 4 variants and stick them on bamboo strips.
During our prep, we had commented (in a half-joking, half-defeatist manner) that if some columns had only 2 or 3 givens, we may as well give up. But it turned out that the actual columns had 7 given digits each, so we gave it a shot.
We started off by identifying the Nonconsecutive columns, which we promptly handed off to Fred, and he put it together. After some time we had the No Three in a Row columns, and High took those columns aside to figure them out. At this point sorting the Windoku columns out should probably have been easy, but I managed to confuse myself, and we ended up wasting too much time on it before getting the right sorting.
Unpeeling the stickers was also taking way too long, as Fred took something like 5 minutes just dealing with the stickers on the Nonconsecutive. There were only 3 minutes left when High finished arranging the No Three in a Row, so we decided to forgo about arranging the Windoku and Antiknight, and finish sticking the No Three in a Row instead. This gave us 2 grids for 600/1200. I suppose avoiding a 0 here was some small consolation, but this should have been finishable if I had sorted Windoku right on my first try. This was especially frustrating for me because our preparation had been adequate, and I just messed it up during execution.
Part of me wishes that instead of stickers, we could have just put tape on each bamboo strip, to which we could attach the columns. It would have saved a lot of time, though perhaps there would have been a risk of the paper getting ripped if we ever transferred columns.
Take-home loot from WSC. I hope I actually find time to solve these.
Watching the playoffs live was also a memorable experience, though I had been hoping for commentary like at some past WSCs. The quarterfinal was contested by 7th-10th placers Can Erturan, Yang Leduo, Thomas Snyder and Martin Merker. Leduo, who is just 12 or 13 years old, won it and proceeded to the semifinal against Ken Endo, Kota Morinishi and Tiit Vunk. For a minute it looked like he might win that as well, but his last grid had a mistake. Kota solved it correctly, which sent him into the final against an all-Chinese lineup of Ming Letian, Dai Tantan, and Hu Yuxuan. The time advantages of each player in the final proved to be quite decisive, with no swaps occurring in the rankings.
Funnily enough, everyone was given a gold medal in their bags. We briefly considered a joke group picture with the medals, but too many people will assume we actually won something, and there's enough misleading news in the world today without us adding to it.
And so my first WSC ended with an official rank of 44th/84 (overall ranking including unofficial players is 58th/152). My main goal had been to raise the Philippine record from 55th, but High did much better by making it to 29th. For team ranking we ended 15th/19 (overall 19/37), which is marginally higher than the previous 17th but is hardly impressive, so there's definitely a lot of room for improvement on future WSCs.
Individual ranks. Each country can only field up to 4 official players for team A. For powerhouses like China and Japan, this means that some excellent solvers are on team B.
Team ranks. We're a long way from the top. (For individual rounds, team score is the sum of the 4 players' individual scores.)
WSC group photo by the organizers.
Looking for more info about the WSPC experience?
- The official website has the instruction booklets (download could take a while) and more details about scores: 2024WSPCWJSC
- Chiel Beenhakker of the Netherlands has a recap on his blog, bakpao's puzzles.
- Germany's team captain Stefan Heine has this video: WSC 2024 World Sudoku Championships 2024 in Beijing.
- Tawan Sunathvanichkul from Thailand runs a blog at Somewhere Over the Rainbow. As I post this, there's nothing (yet?) for this WSPC, but reading his competition reports always made me want to join a WSC someday, and you might have fun reading some of his reports for past events.
Want to get into competitive solving? If your country has a WPF member organization, you can contact them and ask about local competitions. There are also online competitions on:
- The Sudoku Grand Prix and Puzzle Grand Prix, which each run annually with one contest each month (more or less) from January to August, with the finals being held at the WSPC itself.
- Logic Masters India, which has their flagship Sudoku Mahabharat / Puzzle Ramayan series and other contests.
Thanks go to:
- MTG Philippines, for renewing their WPF membership and enabling us to compete as an official team.
- all the people who bought Book 2 of Sudoku for Speedsolvers last August - we didn't have sponsorship, so we appreciated every bit of contribution we could get.
- the WSPC organizers, for making a smooth and very enjoyable event.
- the Almighty God, for working out a lot of things to make this trip possible - everyone's visa and documentation issues worked out, and we didn't experience significant travel problems like flight delays.
And finally, some sudoku puzzles.
These two are Puzzle Expo links for practice puzzles I had written for Rounds 5 and 7:
This last one is not a WSC-caliber puzzle, just something I made for the theme.
Each row, column and 3x3 box must contain the nine letters AEILNTUXY exactly once.
Theme: 2024 WSC podium: Ming Letian (gold), Dai Tantan (silver), and Hu Yuxuan (bronze)
Online Solving: https://tinyurl.com/2c4y5ffx
Classic Sudoku Version (if you would rather solve this using 1-9): https://tinyurl.com/28v4mzp8
Comments ()