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.

PDF

or solve online (using our beta test of Penpa-Edit tools)

PDF

or solve online (using our beta test of Penpa-Edit tools)

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.

PDF

or solve online (using our beta test of Penpa-Edit tools)

PDF

or solve online (using our beta test of Penpa-Edit tools)

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

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: 6/6

Rules: Standard Sudoku rules.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 2:30, Master = 3:45, Expert = 7:30

Solution: PDF

Author’s Note (spoilers): While there are no given sixes in the grid, did you notice that it is very easy to put two sixes into two specific spots?. Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Five Squares

Rules: Standard Sudoku rules.

Answer String: Enter the 3rd row from left to right, followed by a comma, followed by the 7th row from left to right.

Time Standards (highlight to view): Grandmaster = 2:30, Master = 4:00, Expert = 8:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Double Vision

Rules: Standard Sudoku rules.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 1:30, Master = 2:00, Expert = 4:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Big and Small

Rules: Standard Sudoku rules.

Answer String: Enter the 3rd row from left to right, followed by a comma, followed by the 7th row from left to right.

Time Standards (highlight to view): Grandmaster = 5:00, Master = 7:30, Expert = 15:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Logical solving theme

Rules: Standard Sudoku rules.

Answer String: Enter the 5th row from left to right, followed by a comma, followed by the 6th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 6:30, Master = 10:30, Expert = 21:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Besides symmetry, an exclusively logical theme that will be revealed during the solve.

Rules: Standard Sudoku rules.

Answer String: Enter the 3rd column from top to bottom, followed by a comma, followed by the 7th column from top to bottom.

Time Standard: Sudoku Master = 5:00, Expert = 15:00, Novice = 50:00

Solution: PDF and solving video.

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Missing Digit? (opus 2); this avant-garde sudoku poses the question “Is there a 5 in the grid or not?” It is similar to an earlier work by Dr. Sudoku first displayed at the Silicon Valley Puzzle Festival where a different digit, 8, was missing in the same way.

Rules: Standard Sudoku rules.

Answer String: Enter the 1st column from top to bottom, followed by a comma, followed by the 4th column from top to bottom.

Time Standard: Sudoku Master = 4:00, Expert = 12:00, Novice = 40:00

Solution: PDF

Note: This puzzle may seem a bit hard for a Wednesday puzzle, but it is a fun, narrow solving path puzzle with a refreshing theme. The “Time Standard” at this site is used to tell you how hard a puzzle will be, even when the day of the week might be slightly off. Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Countdown to 2013 – this theme is primarily visual, unlike Dr. Sudoku’s earlier Countdown sudoku theme here.

Rules: Standard Sudoku rules.

Answer String: Enter the 3rd column from top to bottom, followed by a comma, followed by the 7th column from top to bottom.

Time Standard: Sudoku Master = 2:10, Expert = 6:30, Novice = 21:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.