[This is a repost from our archives with new notes at the top (original post here): Symmetrically marked cells are one of the easier themes to achieve with Thermo-Sudoku, and in this puzzle the double zeroes highlight a few different kinds of logic to get to the unique solution.]

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

Theme: Double Zeroes

Rules: Standard Thermo-Sudoku rules.

Estimated Difficulty*: 2 stars

Time Standards (highlight to view): Grandmaster = 2:15, Master = 3:30, Expert = 7:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and in Masterpiece Sudoku Mix 2.

[This is a repost from our archives with new notes at the top (original post here): Star Battle, which was originally designed by Hans Eendebak for the 2003 World Puzzle Championship, is one of our favorite object placement styles. The region constraints and no touching constraints lead to a lot of different logic. While there are computer-generated versions of this style in major newspapers now, the hand-crafted themes and logical flows of this puzzle are what we look for with any Grandmaster Star Battle.]

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Theme: Downward Spiral

Rules: Standard Star Battle rules. One star per row, column, and region.

Estimated Difficulty*: 1.5 stars

Time Standards (highlight to view): Grandmaster = 0:45, Master = 1:15, Expert = 2:30

Solution: PDF

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

[This is a repost from our archives with new notes at the top (original post here): Greater than/less than constraints can lead to good forcing chains in different number puzzles. However, I’ve never been a fan of using lots of < and > shapes (particularly when rotated 90 degrees) as that notation only works well across pairs of cells and not across chains of connected cells. I created Thermo-Sudoku as a new presentation method to make multi-cell constraints more easily seen and allow for graphically interesting themes. I first developed the style and name while planning for the book Mutant Sudoku with Wei-Hwa Huang, with imagery of a “melted thermometer in the boiling sudoku solution being poured out on paper” as the first mutation caused by Dr. Sudoku’s mistakes in the lab.]

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

Theme: Grandmaster Puzzles (the G and P shapes in the corners)

Rules: Standard Thermo-Sudoku rules. Range is 1-6.

Estimated Difficulty*: 1 star

Time Standards (highlight to view): Grandmaster = 0:40, Master = 1:00, Expert = 2:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and in Masterpiece Sudoku Mix 2.

[This is a repost from our archives with new notes at the top: This Tight Fit Sudoku (original post linked) goes to eleven! While most Tight Fit sudoku use the range of 1-9, these larger grids — in this case one that has already filled all the “big cells” and only has Tight Fit cells left — can stretch your mind and your notation in interesting ways.]

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or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: The patterned digits in this Tight Fit Sudoku set up an interesting logical solve.

Rules: Standard Tight Fit Sudoku rules. Range is 1-11.

Estimated Difficulty*: 3 stars

Time Standards (highlight to view): Grandmaster = 3:45, Master = 7:30, Expert = 15:00

Solution: PDF and solving video.

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

[This is a repost from our archives with new notes at the top: The final Nurikabe (original post) of week two was one of our “best of” puzzles in our launch year 2013, with an interesting visual clock theme and again a different kind of use of wide open white spaces for that unexpected number (if it was going to be anything, it had to be a 13! There might come a time you might need a clock that can point at that).]

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Theme: Nurikabe Time; don’t wait for the 13th hour to figure out where all the clock islands go.

Rules: Standard Nurikabe rules.

Estimated Difficulty*: 3 stars

Time Standards (highlight to view): Grandmaster = 2:00, Master = 5:00, Expert = 10:00

Solution: PDF and solving video; advice on solving this puzzle has also been posted in “Ask Dr. Sudoku #2“.

Note: Follow this link for classic Nurikabe and this link for Nurikabe variations. If you are new to this puzzle type, here are our easiest Nurikabe puzzles to get started on. More Nurikabe puzzles can be in The Art of Puzzles, in our beginner-friendly book Logic Puzzles 101, and in the e-book Nurikabe by Ashish Kumar.

[This is a repost from our archives with new notes at the top: Just as with classic sudoku, themes that look quite unusual (like separations of kinds of digits, far fewer than just 8 digit types, …, are some rich places to explore Tight Fit Sudoku to come up with something that looks unique. Original link here.]

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: This Tight Fit Sudoku has separate even/odd right/left sides.

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

Estimated Difficulty*: 3 stars

Time Standards (highlight to view): Grandmaster = 2:45, Master = 5:15, Expert = 10:30

Solution: PDF

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

[This is a repost from our archives with new notes at the top: This Nurikabe (original post) still draws from some aspects of Nikoli puzzles at the start, but by the end starts to apply more global constraints and visualization that is very rarely seen from that publisher. Whether this is that they have a different audience than mine or something else is an interesting discussion. Fifteen years ago I learned from many of the styles/ideas they published; one goal of mine is to see that future generations of solvers draw inspiration from my prior work and my own style of puzzle design.]

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

Theme: Imbalance – the lower-left is slightly heavier than the upper-right, and is distributed less evenly, affecting the solve.

Rules: Standard Nurikabe rules.

Estimated Difficulty*: 2.5 stars

Time Standards (highlight to view): Grandmaster = 1:30, Master = 3:00, Expert = 6:00

Solution: PDF

Note: Follow this link for classic Nurikabe and this link for Nurikabe variations. If you are new to this puzzle type, here are our easiest Nurikabe puzzles to get started on. More Nurikabe puzzles can be in The Art of Puzzles, in our beginner-friendly book Logic Puzzles 101, and in the e-book Nurikabe by Ashish Kumar.

[This is a repost from our archives with new notes at the top: Our second week of puzzles paired a puzzle type from another company (see yesterday’s post) with Tight Fit Sudoku, a style I originally created for the book Mutant Sudoku. The style actually framed the whole absent-minded scientist concept behind the mutations, as I “adopted” the Dr. Sudoku nickname for myself by telling a story in puzzle form of a chemist making mistakes that led to inventive puzzles. That book by Wei-Hwa Huang and myself (illustrated and edited by Francis Heaney) is one of the best I’ve been a part of, and one goal in 2023 is to start to republish these works that we have rights back for since they’ve been out of print. It looks like this early GMPuzzle is a bit harder than our standard Tuesday difficulties would become, but that is because I wanted the first puzzle to use a few occurrences of the different kinds of thinking that the “tight fit” rule allows. Enjoy!]

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: Somewhere Over/Under the Rainbow

Rules: Standard Tight Fit Sudoku rules. Range is 1-8.

Estimated Difficulty*: 2.5 stars

Time Standards (highlight to view): Grandmaster = 1:30, Master = 2:45, Expert = 5:30

Solution: PDF

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

[This is a repost from our archives with new notes at the top: Our second week of puzzles started with Nurikabe — a style originally published by Nikoli which is a company that has influenced me and many other puzzle constructors a lot. I expect my inspiration for this first Nurikabe on the site was a lot of diagonal neighbor pair puzzles on Nikoli.com and trying to do some Nikoli-style construction in this genre before pushing to my own, fairly different themes by end of the week.]

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

Theme: Twin Islands

Rules: Standard Nurikabe rules.

Estimated Difficulty*: 2 stars

Time Standards (highlight to view): Grandmaster = 0:45, Master = 1:30, Expert = 3:00

Solution: PDF

Note: Follow this link for classic Nurikabe and this link for Nurikabe variations. If you are new to this puzzle type, here are our easiest Nurikabe puzzles to get started on. More Nurikabe puzzles can be in The Art of Puzzles, in our beginner-friendly book Logic Puzzles 101, and in the e-book Nurikabe by Ashish Kumar.

[This is a repost from our archives with new notes at the top: Just as I mentioned three days ago repeating prior Sudoku themes when I get back into writing in a puzzle style, “Rhyming clues” is one of the five or so “canonical” TomTom theme ideas I’d explore time and again in books like the original TomTom Puzzles. This last puzzle of our 2013 intro week is such an example although did not resolve as cleanly in the middle as other gems I’ve unearthed during TomTom exploration. I’m very hopeful that 2023 may finally be the year to revise and expand the original TomTom puzzles book I wrote in 2009, since it has been out of print for awhile.]

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

Theme: “Rhyming clues” – almost all clues here in this TomTom are presented with identical neighbors.

Rules: Standard TomTom rules. Range is 1-8.

Estimated Difficulty*: 4.5 stars

Time Standards (highlight to view): Grandmaster = 9:00, Master = 15:00, Expert = 30:00

Solution: PDF and solving video.

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