Two more from the US Sudoku Qualifying Test in May — both geometric departures from regular sudoku.

As I consider the 2012 Irregular on the USSQT one of my best puzzles from that year, it was obviously going to be a challenge to do as well this time around. I felt the puzzle below was an adequate follow-up but certainly not as good as last year’s. The solve is meant to take advantage of the slightly irregular spacing of 1-6 in the patterned middle with the extra 7’s and 8’s giving a single solution. Note there are no 9s anywhere in the grid. Some Law of Leftovers steps will likely be encountered before the finish.

For the isodoku, just before the US Qualifier test, one of our readers here suggested I make a tutorial on some of the forced rules that come with these 3d shapes (this was after an isometric TomTom that strongly required solvers to know only 2 of each digit could appear on each face). I obviously couldn’t post such a tutorial just before the USSQT, but the properties of the 3D shapes was strongly in mind here. Often — like in the standard 2×4 rectangle form of an isodoku, or the 2012 USSQT Isodoku — there is a strong 2×2 square requirement that can split the digits into two distinct sets throughout the puzzle (see this colored solution of the 2012 for example). This year I wanted to choose a geometry that almost seems like it needs that 2×2 requirement in places, but here only three digits are highly constrained and the attempt to split the shape into patterns falls apart. Can you spot the three constrained digits and sort out where they must always go in this kind of geometry? Six particular cells are key.

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Theme: Pattern in regions and digits

Rules: Standard Sudoku rules. The regions are not 3×3 boxes but are instead irregular shapes indicated by the bold lines.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Solution: PDF

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Theme: Stacked boxes

Rules: Standard Isodoku rules, using numbers 1-8.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Solution: PDF

Two more from the US Sudoku Qualifying Test in May — both are styles I’ve constructed a lot of in the past and will likely continue to construct a lot of in the future as they are both pretty simple variations that add more properties of the numbers into the logic of sudoku and enrich the solving experience.

I went for a lot of less common symmetry types with this test (diagonal or mirror symmetries instead of 180 degree rotational) and both of these themes showcase one of those less common types. With Tight Fit, the diagonal symmetry works well with the added slashes forming their own diagonals parallel to the mirror plane. The solve was meant to fairly easy, but the sparsity of starting digits here actually leads to a rather large cycle to place two of the highest digits remaining towards the end of the puzzle. This trait pulled it towards the top of my pile of Tight Fit to include here.

For the Consecutive Sudoku, I’ve been doing a fair bit of half consecutive/half non-consecutive exploration recently (such as this earlier GMPuzzles one). And I’ve played with 2×2 box shapes with consecutive bars before too, such as here. Well, it turns out that there are no puzzles possible that have just the 2×2 box shapes in opposite corners as in the second linked puzzle without additional bars elsewhere. But there are a whopping 4 possible solutions with the repeated top boxes and no other bars as here (and 2 of those 4 are trivial copies from a 1-9 to 9-1 swap). It was from that small set of potential solutions that I crafted this puzzle. Using a given presentation that evokes the same kind of bars as up top seemed best and gave the solving properties I wanted. But if you’d like an extra hard challenge different from this one, put a single 1 in the lower-left corner and try to solve from there. As I’ve discussed before, the non-consecutive constraint is really powerful and constraining in ways you wouldn’t expect but it always needs some hands-on work to cultivate a fun and approachable puzzle.

Both of these puzzle are probably on the easier end for this test, but both are good representations of the new logic that arises from the variation. As “extras” from the first Grandmaster Puzzles construction cycle, it seems fitting to get them both up here now.

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Theme: Diagonal Series

Rules: Standard Tight Fit Sudoku rules. Range is 1-9.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Solution: PDF

PDF

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Theme: Boxes of Two Sorts

Rules: Standard Consecutive Sudoku rules.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Solution: PDF

The Sudoku Grand Prix (GP) has certainly now shown a variety of test styles after the creative but unorthodox Turkish test this past weekend. I’m still not sure exactly what the GP is trying to be, and I have no idea what the “playoff” in Beijing will look like (does anyone know anything about the rules or puzzle designers?), but the list of 10 competitors to qualify is getting much clearer now. Quite incredible to have a different winner for each event so far.

Our test, like some others in the GP such as the UK test, had a pretty clear goal to have a lot of elegantly constructed sudoku in pretty simple styles to test basic sudoku skills. All our puzzles had fair, logical solution paths, and we expected many solvers would finish. And as I still think of this as a US Sudoku Qualifier first, and a GP contest piece second, I was glad we got two of the qualifying Americans to submit all of the answers even if one had a mistake. While this is now quite belated, congrats to Jason Zuffranieri for his US victory and to Bastien Vial-Jaime for the overall victory.

Here is the second pair of classic sudoku that appeared on that contest.

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Themes: Both geometric and logical

Rules: Standard Sudoku rules.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Design Notes (highlight to view): The third classic sudoku (and first here) was built around an even versus odd theme and recognizing this unusual partitioning of the digits will be key to making fast progress. A bunch of singles (either naked or hidden) can be found based on parity around the middle sections which finally breaks through to the final solution. The fourth classic sudoku (and second here) was constructed to have an early and pretty clear single sticking point aspect to it. The geometry suggests something should be present in the almost full rows or columns. If solvers focus on those most constrained positions in the first column, they will find a naked pair [89] that gets the whole solve going. While none of these classic puzzles required extremely difficult techniques, keeping the solving paths somewhat tight at the very start makes them good competition challenges in my mind.

Solutions: PDF and PDF

While scheduling the month of June for the site, and considering the potential for some likely downtime or errors while changing web hosts, I budgeted two weeks for recent US championship puzzle discussion. For this week, I’ve planned to cover the US Sudoku Qualifying Test (also the sixth leg of the Sudoku Grand Prix). If you are desperate for new puzzles, those will arrive next Monday at their usual time. But there may be some new challenges revealed throughout this week during the discussion of these creative sudoku.

I figured I’d give a general overview of our design process at the start. As with past years, we (Nick Baxter, Wei-Hwa Huang, and myself) had planned a two-part championship with Classics and near classic variations for the first part, and mostly new or less common styles for the second part. Some of this has been to gauge relative solving capabilities on the challenges that might appear at a WSC, and some of this has been for our own sanity checking of potential competitors. There are more web-accessible sudoku solving tools that can handle “part 1” puzzles and some unbelievable times have been posted there in the past. But less familiar or original styles in “part 2” will challenge anyone solving with certain types of assistance. After the 2009 experiences in Philadelphia at our last live national championship, we know to be extra cautious.

While having two parts was the original plan, the requirements of the Grand Prix changed our design mid-stream and a single big round was used instead. So solvers got 2.5 straight hours of solving to test their mettle. But you can see that the ordering of the puzzles still naturally splits the first ten from the last ten and perhaps many solvers found themselves focusing on just the first part instead of the other.

We like having a mix of puzzles but also a fair number of classic sudoku since a sudoku championship should certainly test the fundamentals. I wrote all 4 of our classic puzzles, each somewhat noteworthy in its own way. Their numbering was maintained in my “construction order”, as testing revealed their mean solve times were within a minute of each other and they would all receive the same point values on the test. I believe only solvers with a very broad skill set would have a uniform performance on the entire set. But just as different test-solvers reported being tripped up by different puzzles, competitors reported the same thing with #2 and #4 seeming to be outliers. I wonder what your experiences were?

I’m posting the first two classic puzzles below, with design spoilers concealed after each puzzle. The next two classics will follow tomorrow.

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Themes: Both geometric and logical

Rules: Standard Sudoku rules.

Answer String: For the USSQT, the answer strings were a set of rows/columns encountered late in the puzzle. For this week, you can just hit the solved button on an honor system if you think you’ve solved it.

Design Notes (highlight to view): The first puzzle was designed around a low/middle/high separation and has large squares made out of 1-3 and 7-9 only that provide some symmetry along the solve. For example, consider the 1 in the upper-right corner and the 9 in the lower-left corner which come from looking horizontally, followed by either 79 or 12 pairs to finish those border columns from looking vertically each allowing the last two numbers in the corner regions to be identified. This is probably the easiest of the four classic puzzles but not by much. The second puzzle was designed to require good use of pointing pairs, particularly in the upper-left boxes, involving the “8” and “9” that are lone digits. A relay of these pointing pairs through two boxes should place the first 8s and 9s that cascade to give several other digits.

Solutions: PDF and PDF

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Theme: Triple Play

Rules: Standard TomTom rules, using digits from 1-9.

Answer String: Enter the 4th column from top to bottom, followed by a comma, followed by the 6th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 12:30, Master = 25:00, Expert = 50:00

Solution: PDF

Note: Follow this link for other classic TomTom. If you are new to this puzzle type, here are our easiest TomTom to get started on.

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This is a “Franken-Friday” puzzle variation.

Theme: Plus Signs

Rules: Standard Shape Sudoku rules.

Answer String: Enter the 9th row from left to right, followed by a comma, followed by the 4th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 7:00, Master = 15:00, Expert = 30:00

Solution: PDF

PDF

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Theme: Logical

Rules: Standard Tapa rules.

Answer String: Enter the length in cells of each of the shaded segments from left to right for the marked rows, starting at the top. Separate each row’s entry from the next with a comma.

Time Standards (highlight to view): Grandmaster = 1:15, Master = 2:30, Expert = 5:00

Solution: PDF

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between a composite mode for line/edge drawing and a number entry mode.)

Theme: 28 “dice”, opus #2 (See here for the first in Grant’s 28-given series of Fillominoes.)

Rules: Standard Fillomino rules.

Answer String: For each cell in the marked rows/columns, enter the area of the polyomino it belongs to. Start with the 5th row, followed by a comma, followed by the 9th row.

Time Standards (highlight to view): Grandmaster = 2:20, Master = 3:30, Expert = 7:00

Solution: PDF

Note: Follow this link for other classic Fillomino and this link for more variations on Fillomino puzzles. If you are new to this puzzle type, here are our easiest Fillomino puzzles to get started on.

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Theme: Deja Vu?

Rules: Standard Slitherlink rules.

Answer String: Enter the length in cells of each of the internal loop segments from left to right for the marked rows, starting at the top. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 1:10, Master = 1:30, Expert = 3:00

Solution: PDF

Click here for larger image

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Logical theme encountered during the solve

Rules: Standard Masyu rules.

Answer String: Enter the length in cells of the horizontal loop segments from left to right in the marked rows, starting at the top. If the loop only has vertical segments in the marked row, enter 0. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 8:45, Master = 11:00, Expert = 22:00

Editorial Note: This is our first Giant puzzle from Grant. Not because he hasn’t been writing many; we’ve been keeping most of his giants for The Art of Puzzles so consider this a teaser for some of the great puzzles that will be in that collection.

Solution: PDF