A Miracle Thermometer Sudoku

*** TODAY'S PUZZLE ***
Some recommendations are so fulsome that we obey them instantly! Marty Sears told us this sudoku by Michael Lefkowitz ("juggler") was a stone cold classic and so we had a go. You'd be correct in thinking that the grid seems rather empty and the rules somewhat open-ended but there is a unique solution and it is humanly-findable!!

(During editing we noticed a small logical error very late in the video (58mins) right as Simon says "That's the droid we're looking for" (it turned out it wasn't the droid after all!!). The puzzle is virtually solved at this point but, in case anyone is interested, the easy way to continue without the error is to notice that r1c7 could not be a 5 at this point as it could not attach to a 6. No droids were harmed as a result of this error but Simon apologises nevertheless.)

Play the puzzle at the following link:

Rules:
Fill the grid with the numbers 1-7 such that no number repeats in a row or column. The grid is completely covered by thermometer lines. You cannot see them because they are invisible. Nevertheless, numbers increase along thermometers starting from their bulb end. Thermometer lines move orthogonally and diagonally, and do not cross themselves or other thermometers, except at the white diamonds, where they must cross themselves or another thermometer. Thermometers do not pass through Xs. Thermometer bulbs do not touch each other, even diagonally. All thermometers have the same length.

You can find Delia's recipe for Chocolate Guinness Cake here (but remember: no walnuts and double the icing):

*** ROLLER COASTER NURIKABE by the_cogito ***
Simon's 2.5 hour solve of Roller Coaster Nurikabe by the_cogito is now available on Patreon. Check the puzzle out at the link below:

Also there's our January Patreon competition: All The Fun Of The Fair featuring sudokus themed around fairground rides!

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▶ Contents Of This Video ◀

0:00 Theme music & Puzzle intro
1:45 Magic Square Scrabblegram
3:26 Watercoloured Simon
3:41 The World's Best Chocolate Cake?
4:34 Broken Secrets by TotallyNormalCat
5:09 Happy Birthdays
7:35 Rules
10:57 Start of Solve: Let's Get Cracking

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[thejuggler]

I'm so glad you enjoyed my puzzle!

It's certainly an honor to be in a CTC video, I really am chuffed to bits. I have more in the works that take this concept even further, so stay tuned. :)

[theodosiskostouros]

Loved the puzzle! Absolutely brilliant! However i think the reasoning that allowed you to complete the final stretch of the puzzle at 58:19 doesn't account for the fact that the 6 in R4C6 could get a 5 from R4C5. I don't really know what the correct next step would be in that part of the puzzle but I'm confident you would have figured it out if you gave it a bit more thought. Very enjoyable watch as always!

[bobfish]

@58:20 - Lucky guess - There was another 5 to the left..

[freya]

I loved this puzzle, I made the colloring less confusing by just having 2 collors, 1 for low(123) and one for high(567). It also helped make some deductions easier because i knew there had to be 3 of each collor in every row and column

[rainerzufall]

A faster argument for not having 49 thermos, is, that the 49 bulbs have to be separated, which is not possible!

[monkeyunit]

Love it when the puzzle takes a certain direction and I'm like: Simon will pull out his lovely box of crayons and start colouring any minute now

[MateiGall]

Little mistake at 58:18; the 6 can get the 5 also from r4c5. But the 5 in r1c7 has no 6 near it, so it forces 2 in r1c7 and a 5 in r3c7.

[martysears]

So pleased that this got featured, these kind of geometry puzzles are my absolute favourite... great solve from Simon too - he did it pretty much exactly the same way I did, but he made fewer mistakes than me! Well done Michael, look forward to more of your puzzles

[KevFrost]

There's a previous Simon technique that I used: Given that each thermometer is always 1-7, each end must be either 1 or 7 and these are interchangeable if we ignore the bulb rule. So lets assume r1c2 is a 1 as a placeholder, then we can change all 1s to 7s, all 2s to 6s etc when we have the final disposition of thermos when we can see whether the bulb rule makes the "1" end or the "7" end the bulb

[NettoTakashi]

Where Simon started using colors, I switched to placeholders-- letters A through G, where A and G were 1 and 7, B and F were 2 and 6, etc. This helps keep the relationship between different cells clear-- A is consecutive with B is consecutive with C, etc.-- while keeping track of the fact we don't yet know which ends of the thermos are the bulbs and which are the tips.

[pzaan]

This certainly seemed like an opportunity for coloring and placeholders. I settled on separate coloring for each thermo line and then added orange / blue shading for digits above and below 4. The line colors made it easier to see what fragments might connect to each other. (And made the logic assumption in 58:19 stand out.) Loved the puzzle and the way you could progress from the left corners to the rest of the grid.

[laincoubert]

what i absolutely loved about this was how every single time i expected a line to go a certain way because of other information the line went in a totally different direction (upon other deductions). it's easier to just do sudoku at the very end and then be surprised how all of the lines connect

[Ciiran]

Loved this one. The most difficult puzzle I've ever managed to solve without help from Simon. I went in exactly the same path as him, but much slower since I had to back up and rework several parts when I encountered conflicts.

[RoselynTate]

I think my colouring choices made this puzzle a lot easier for me -- I decided to leave 4s white, like Simon, and then I used (slightly simplified for lack of indigo/violet distinction on the colour palette) colours of the rainbow, and then I put them in order -- red, orange yellow for 17, 26, 35 on one side of 4, and then green, blue, purple for 35, 26, 17 on the other side. It turned out quite pretty, and the fact that I happened to make 1s red was a bonus, lol, but having the colours have an order naturally in my brain made this puzzle a lot less head-wrecking -- watching Simon's solve is breaking my brain a little bit simply because I'm struggling more to keep track of which colours go into which.
Final time 28:22 for me!

[hockeyhacker]

34:57... How long is it going to take him to notice where the 4 that connects to the orange in the diamond because it can't connect to the 4 that is already there because if it did the thermometer would have to split in two and snake. and so there is a given 3rd 4 that has been there for a very long time at this point.

[holliambria]

This way of coloring is so much clearer than what I did!

[estherwestbroek]

Did it. Took extra long to have 7 different colours and 7 differently coloured lines. It lookes beautiful!

[marklindsey]

Please don't beat Simon up about the 65 @ 58:18. Simon caught it during edit and put the logical solve path in the video description. is limited.

[markp]

34:17 finish. I colored my pairs as high-4-low instead of individual colors. It was a lot easier for me than remembering which color leads to which color on the thermos. And I missed the logic that Simon found @55:55, but was able to solve without using it fortunately. It clicked with me almost immediately that the puzzle had to have a pair of 7s touching, or it would be able to flip thermos. But I was surprised that it resolved itself as early as it did. Such a fun puzzle, excellent!

[adagraves]

Took me over twice as long. Though impressed myself with how quickly I got that the thermos had to be size 7 and that got me a 17 pair in the bottom left almost immediately.