This is part 2 of 2 about my experience at the 2018 World Sudoku Championship which happened on 4-7th November 2018 in Prague, Czech Republic. This second part will be a breakdown of my thoughts on each round.
Round 1 – Classic Start [Individual]
Me and Sinchai correctly predicted 13 puzzles with the givens forming numbers 1-13. 30 minutes was going to deplete fast and I started panicking when my second grid had an error. Quickly recovering, I turned in a 9/13 puzzles where my 10th puzzle needed about 20 more seconds.
I was quite confident in classics but having stumbled I was therefore surprised to finish in 17th. Wow!
Points: 240/345 – 17th place (unofficial ranking which includes non A-team members)
Top score: 325 by Jakub Ondrousek
Favourite puzzle: I don’t think any fast solver would remember any particular grid.
Round 2 – FED Alternatives [Individual]
Disaster. Things went wrong from the get-go. I was slow to unravel the easy-pointers, broke Diagonal Sudoku twice, broke Windoku and now after reflecting back on this round, I still don’t know what exactly went wrong. I can’t think of a time where I would place 120th in any sudoku competition. Point-wise, I dug myself into a pretty big trench. After screaming into a pillow, I right the ship and scored a personally satisfying result, including two top-20 finishes, for the remaining 4 individual rounds.
Points: 160/515 – 120th place
Top score: 585 by Tantan Dai
Favourite puzzle: The cross-theme was pretty cool
Round 3 – Krtek’s Cup [Individual]
After a bad round 2, I switch to a conservative strategy. I sprint from front to back skipping Irregular Dots and Football. After securing a cushion of points it was time to tackle the big grids. The grids were great and you could not ask for a cleaner solve. I purposely slow down during the high-pointers as to not make silly mistakes. As a result of adjusting to a defensive strategy – I was error-free on day 1 (with the exception of round 5 where I wasn’t expecting to be correct after guessing towards a solution having only a minute left). Certainly a nice round with a pleasant variety of genres.
Points: 735/1180 – 20th place
Top score: 1115 by Tantan Dai
Favourite puzzle: Killer 007 and Non-Consecutive Spiral
Round 4 – Arrow Style [Individual]
Before this round, results for round 1 were posted so I was very inspired to make up for the terrible crash in round 2. Count the Odds was going to be very guess-y so after sprinting from the front I started chipping at the Morse Sudoku. I wrote a practice puzzle for this and knew that you had to carefully keep track of the odd/even cells. This round was very kind to me and resulted in my third top-20 finish out of 4 rounds. Half of the puzzles had the same layout of arrows which made for a pretty theme.
Points: 290/430 – 17th place
Top score: 430 by Tiit Vunk and Kota Morinishi
Favourite puzzle: Morse Sudoku
Round 5 – Growing Regions [Individual]
A cute round. I love Surplus/Deficit sudokus ever since I saw them in Mutant Sudoku (by Thomas Snyder and Wei-Hwa Huang). Tom Collyer always include these in the UKSC and I even wrote a few of them for a few issues of Sudoku ve Otesi.
However the competition puzzles were tough. Because the round was so short, I hacked through most of them by guessing. A suggestion is that if you can’t fill in a digit in 60 seconds: guess away!
Points: 225/310 – 27th place
Top score: 380 by Jan Mrozowski
Favourite puzzle: The 6×6 irregular was nice
Round 6 – FED Variants [Individual]
The heavy-pointers here were very systematic. Step by Step could’ve used a better example in the IB and the actual puzzle was fun. Again, I tried not to get too far ahead of myself and carefully work front to back. Offset was probably undervalued. I had about 8 minutes to wrestle with Makodoku but could not see the early error where I had 2-3 as a + (and not x). Disappointing since this was one type I had planned to tackle. As for the 150-point Cave, I waved goodbye at it even before arriving into Prague.
Points: 320/650 – 28th place
Top score: 580 by Kota Morinishi
Favourite puzzle: Odd-Even Killer
Round 7 – Flip-flop Classics [Individual]
The practice puzzle from the IB never got cut out as I carried it with me wishing that one day I’ll get around to solving it. A vain effort. Sinchai studied this intricately and gave some helpful tips, although bluntly, I’m not too optimistic going into this round.
This reminded me Beijing 2013 WSC’s round 3, where we had to reconstruct a broken Expanded Sudoku. A lot of strong solvers end up with zero as Kota did here as well. About 7 minutes in, I was blissfully convinced I had the right flip-flop pattern. Then a contradiction hit me like running into a wall. By 10 minutes, I had accidentally ripped one “wing”. As there were no replacements I pretty much surrendered to inevitable defeat.
Points: 0/120 points
Top score: 220 by Bastein Vial-Jaime and Jan Mrozowski
Favourite puzzle: There was only one puzzle so…
Round 8 – Two Pairs [Team]
As mentioned in part 1, we formed our team (UN-09) way back at the airport since Team India conveniently had 2 leftovers. Jaipal Reddy and Ezhilarasi Mathavan not only became our teammates but also our benchmates in the competition hall.
Without a proper team, I never gave the Team Rounds a chance, ie. I didn’t even bother looking at the IB. Fortunately Sinchai was more diligent and took only a few minutes to brief me on the ins-and-outs of the types that were to appear in round 8.
Round 8 had 12 puzzles split into two pools of 6 where two solvers would swap over solving in 10 minute intervals. We never got the opportunity to have a planning session with Jaipal and Ezhilarasi but luckily we were on the same wavelength. There are two members that would never meet throughout the rotation cycles so me and Sinchai would take those two roles. We roughly mapped out which type we would leave for other guy since our fortes don’t overlap. Sinchai likes the math-heavy variants and I’m more of a puzzle guy, so this explained why we might have been a little bossy when it came to choosing which puzzles to solve. This tactic worked like a charm and we scored a very credible 12th equal, just 50 points shy of India’s A team.
Individually, Jaipal finished 78th and Ezhilarasi 207th. It is surprising they didn’t finish higher because after 3 team rounds with them, I genuinely thought they were very decent solvers. Jaipal would pick up my careless mistakes when I got too fast, even finding some crucial deductions before I did. Meanwhile, Ezhilarasi is very fast at classics, probably too fast as her blazing handwriting would later become very hard to read. So I would find certain digits using the variants’ rules and she would promptly vacuum up the other part of the grid using classics. We had about 1-2 minutes left and guessed at the Unique Rectangles which wasn’t that heart-breaking when it was graded wrong.
Points: 1300/1900 – 12th place (out of 62 teams)
Top score: 2100 by Germany A
Favourite puzzle: Pyramidal
Round 9 – Killer Style [Individual]
Day 2 started with this round and I was still keen on minimizing risks. After seeing the first Arrow Sudoku in round 4 (which was basically a classic), we correctly predict that the first Killer sudoku would also be a classic in disguise. I ran through the round consecutively before halting at Ordering. After seeing no clear deductions, I gambled by inserting the most likely plausible tens digits of each 1×2 cell. Eventually, I would hit a snag but was hoping that tweaking would squeeze me out of any contradictions. After about 5-6 minutes I knew it was time to abandon ship. I motored through Odd Even Sum by using parity rules. To accelerate the solving process, you had to turn the puzzle into an Even-Odd Sudoku, and later it becomes much easier. Different Around was not on my agenda but Sinchai did manage to hack his way through it. Later at lunch, we tried solving Different Around without bifurcation and found that the solving path, albeit narrow, was reasonably fair. The cages and givens had near-identical patterns throughout the round, so another creative theme.
Points: 260/450 – 26th place
Top score: 450 by Bastein Vial-Jaime
Favourite puzzle: Odd Even Sum
Round 10 – WPF Grand Prix [Individual]
Up to this point I was content with my performance, turning in no careless errors. My biggest mistakes were to come in these last two rounds costing me a spot in the top 30. This round included variants that appeared in the Czech leg of the GP. Again, I continued to solve this round in order, skipping Scattered Irregular, which I felt was a type I am slow at. Duodoku required multiple revisits but fell neatly. Disparity took some time but my new notation technique of crossing the evens and circling the odds made the puzzle easier to visualize. Now onto the toughies.
I studied Sum Sandwich and Bust carefully and still scored 0 from these two valuable grids. From writing a practice puzzle beforehand, Sum Sandwich went smoothly for me from start to finish. Alas, somewhere I had made an incorrect assumption and my answer had an extra valid sum that had to appear outside the grid. As for Bust, I couldn’t even fill in the first digit. This translated to a period of about 15 minutes lost in the time-space continuum with no points to show for. That lost time could’ve saved my partially-filled Diagonal Consecutive and likely still have time to finish Scattered Irregular.
Points: 375/790 – 51st place
Top score: 705 by Kota Morinishi and Shiyu Chen
Favourite puzzle: Diagonal Consecutive (solved after the competition)
Round 11 – Czech Grand Prix [Individual]
Last round! Solving in order meant the Interconnected Classics was the first obstacle. Together the two grids total 80 points so it was a difficult puzzle by that standard. After that fell, I floored through all the easy-pointers omitting 3D-sudoku and Prague Star, somehow I couldn’t find any clear solution to both of those. I spent about 9 minutes slowly chipping away at the 12×12. That too fell. Frustratingly, when I got my papers back, I had made my first and only silly error of the entire WSC. I had an easily-mendable duplicate. 120 points vanished into thin air.
Another avoidable setback came in Full Rank. Somehow I had thought the value of each row and column only applied to the first three-digit (correct was all 9 digits were to be taken into account). The IB miraculously didn’t require more than 3 digits for the puzzle to be solved. Which meant after reaching a point where two 3-digit numbers (from different row and column) were identical, I thought I had made a mistake. Looking for the mistake that didn’t exist, I incorrectly assumed I had broken the puzzle and moved on.
Points: 390/810 – 48th place
Top score: 730 by Tiit Vunk
Favourite puzzle: One Bug per Line was an interesting type
Round 12 – Mysterious Samurai [Team]
Here teams had to figure out which rule applied to which grid of the 4 samurai sudokus, before completing each big puzzle. We tackled this in order and couldn’t really make much progress. Sinchai would take a step back and try to determine the rules while the rest of us would try to fill in as many digits using just the classic sudoku rules.
We were very slow to make inroads and even when some rules were certain, the little-givens meant that the puzzle still didn’t budge.
We managed about 1 and half samurai sudokus when the round was over. A hard round which is made more difficult by having to crane over each other looking at the same A4 sheet which we sometimes have to look at sideways.
Dismal result as a lot of our grids had minor errors.
Points: 225/1625 – 42nd place
Top score: 1025 by Poland A
Favourite puzzle: too hard
Round 13 – Coded [Team]
This round had 4 puzzles where letters in the grid stand for the same number throughout the 4 puzzles. There were 4 sets, totaling to 16 puzzles. The plan was to run through each letter and shout out which numbers could not stand for that letter, based on each individual’s grid. We were slow to start and after finishing our set of classics, we got into our rhythm and quickly finished the Irregular set. In the last few seconds we also finished the Differences set. We had 2 errors so a 10/16 result.
How surprised we were when we found out our result was good for 4th place. Naturally I thought there was a marking error but after rechecking with the excel sheet; it was because the top titans took risks by starting with the Skyscrapers set and most only managed to get to Differences, working from back to front.
4th place just behind Germany, China and Japan!?
I’ll take it!
Points: 925/1600 – 4th place
Top score: 1200 by Germany A
Favourite puzzle: Differences set
Individually, a rather whimper of an ending in the last couple of rounds. Nonetheless the few top-20 scores were enough to console me for future sudoku competitions. The puzzles were very nice and I even had time to notice some of the recurring themes in each round. Big ovation to the authors!
Short thoughts on WPC
As previously mentioned, I helped with test-solving this year. Points were not yet assigned so diving into each puzzle I had no idea what to expect. But I did notice a peculiar recurrence. The difficulty levels of each puzzle were quite bimodal for each set. Often, I would find puzzles that took 2-3 minutes to solve and the remaining puzzles took something like 10-15 minutes. There were no in-between!
At the time of writing, there is only one WPC recap (from Robert Vollmert). Reading through that, one sentence resonated with me very much: “…These fully clued puzzles were a theme throughout the contest, presumably a consequence of the construction style of starting with a solution grid, adding all clues, and verifying that you end up with an ok puzzle”
To play devil’s advocate, some authors do approach puzzle construction this way. David Millar stands out when you look at his sudokus. It might be a matter of taste, but I find backtracking (deriving a puzzle from a valid solution) hardly produce elegance. There were a lot of Latin Squares with full clues this year and the Skyscrapers round was filled to the gills with such.
The Variation and Innovative rounds were brimmed with exotic puzzle types. Newcomers would be forgiven if they sulked. On a brighter note, the puzzles that were made conventionally had some nice break-ins, not to mention there was a copious amount of new ideas waiting to be explored.
Final thanks to the organizers for a wondeful time in Prague.
Hope to able to join the fun in future WSC/WPCs!