The Hardest Sudoku Of All

*** Today's Sudoku ***

Let's start with an apology. As Simon says during the video, he is incredibly concerned about taking too much of people's time and recognises the ludicrous nature of the length of tonight's solve. He attempts a puzzle by Gliperal called Balanced Loop Sudoku. This is an astonishing construction and undoubtedly sits in the pantheon of puzzles that can be described as "One of the greatest ever". BUT it is NOT easy. It is definitely worth checking out the example on the Logic Masters Germany link below if you're in any doubt about the rules. Having done that, strap yourselves in because this one is brain-frying!! Play the puzzle at the link below:

Rules:
Normal sudoku rules apply. Draw a single closed loop that travels orthogonally through the centres of some cells. The loop does not use any cell more than once and must travel through each dot. The two loop segments extending from both sides of a dot must be balanced ie the sum of the digits up to and including the digit in the cell containing the first turn must be the same. ALL possible dots are given.

Example Puzzle:

*** More Patreon Content ***

To all our patrons - thank you so much for your support.

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- Simon's solve of Fillomino Aquarium - the new beast of a puzzle by Phistomefel.
- Mark's latest solve of The Times Club Monthly Special crossword.
- the complete suite of solution videos (all 45 of them!!) to the Pyramid Puzzle Hunt.
- January's monthly reward: A Star Wars themed sudoku hunt by Peter C Hayward.

Coming Soon: The QAS ("Quite Approachable Sudoku") Hunt! 1 Februrary :)

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Play the puzzle in the video by clicking the link under the video (above). We are building a website which will allow you to enter your own sudoku puzzles into the software and this is coming soon!

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Melvyn Mainini

[Gliperal]

Since you say self praise is no praise, allow me to do it for you: This was a fantastic solve! Of all the people I've watched attempting the puzzle, you've certainly picked up on the fundamental ideas the fastest. Even the people who testing this puzzle on the discord server took several days, and only one of them was able to solve it, even with hints. Not only that, but there are a few ways to bash through some of the sections of the puzzle, and your intuition for logical tricks lead you to almost exactly the path I was hoping solvers would find.

I know long videos and difficult puzzles can be stressful, but I cannot express how elated I felt watching this solve. When I was first playing around with this ruleset, so many interesting tricks and ideas surfaced that I couldn't help but include them all. The parity logic on the left side of the puzzle. The 2 cells that are equal to 3 cells equal to 4 cells equal to 5/6 cells. Situationally including or excluding dots from the balance calculations (sometimes both at once). The logic with the central cell in a box having to extend 2 in at least one direction was really fun, because it mimics the nature of black dots in typical balance loop puzzles. It would have perhaps been more fun for solvers to have a set of this sort of balance loop puzzle: one easy one to get the fundamental ideas, and then some trickier puzzles each showcasing one of the techniques/ideas clearly telegraphed. If I were a better setter I probably would have done that, but ultimately I took a gamble. As a result, this puzzle (and therefore the techniques) almost fell into the depths of obscurity, which is why it fills me with such joy to see you not only succeed but hit upon exactly the tricks and ideas that I was hoping to display. I can only hope that other people get as much joy in seeing you find that sort of logic as I do.

Also, don't think I didn't spot that the CTC logo in the thumbnail is balanced. Very cheeky Simon. :D

[Adrian_Grey]

Simon: "here's a two hour video of some nerd solving sudoku"
40, 000 other nerds: "where's the popcorn?"

[SnowTheJamMan]

When will Simon learn that these long videos are not only not boring, but extremely entertaining for the huuuge majority of us

[bluji]

Simon should just realize by now that no matter how long the video, we'll watch it. Lots of love to our brave sudoku warriors at CTC! <3

[brianshilling]

I mean this with absolute respect.

Don't be a dingus.

We love watching you spend two hours on a puzzle because it saves all of us 8 hours trying to do the same thing. Plus we all get the tiny bonus dopamine when we see the rare obvious thing before you do. <3 Thanks for all the dopamine hits over the past year I've been watching.

[inspiringsand]

Rules: 04:06
Let's Get Cracking: 09:01
Puzzle Solved: 2:15:55
Simon's time: 2h6m54s

What about this video's Top Tier Simarkisms?!
Bobbins: 3x (21:16, 58:02, 58:05)
Phistomefel: 2x (00:48, 03:09)
​Scooby-Doo: 1x (38:14)

And how about this video's Simarkisms?!
Sorry: 23x (21:18, 27:16, 38:55, 47:20, 50:52, 50:55, 1:00:44, 1:04:11, 1:07:21, 1:07:21, 1:09:06, 1:09:06, 1:17:03, 1:17:53, 1:18:13, 1:19:06, 1:28:26, 1:50:46, 1:56:49, 1:56:53, 2:04:34, 2:05:41, 2:11:13)
Hang On: 15x (04:57, 27:24, 34:07, 53:34, 53:34, 1:12:23, 1:12:23, 1:18:32, 1:21:56, 1:22:10, 1:26:40, 1:31:28, 1:46:27, 2:09:02, 2:14:47)
Wow: 13x (07:35, 34:43, 34:43, 34:43, 56:58, 57:00, 1:23:22, 1:27:15, 1:44:26, 1:47:34, 1:59:39, 2:01:10, 2:04:50)
Beautiful: 12x (29:42, 42:06, 42:07, 1:30:32, 1:31:22, 1:31:22, 1:34:04, 1:37:26, 1:43:45, 1:47:11, 2:00:59, 2:05:28)
Good Grief: 11x (46:12, 1:06:04, 1:18:25, 1:31:00, 1:34:04, 1:40:54, 1:41:56, 1:59:39, 2:02:10, 2:05:28, 2:15:26)
Nonsense: 10x (21:20, 33:37, 37:53, 50:18, 50:55, 54:53, 1:13:58, 1:14:04, 1:30:00, 1:33:53)
In Fact: 9x (09:10, 26:18, 37:20, 39:39, 1:42:06, 1:42:50, 1:42:50, 1:47:09, 2:15:42)
Obviously: 8x (00:34, 18:11, 28:31, 31:42, 56:07, 57:14, 1:14:34, 1:40:46)
What on Earth: 6x (04:41, 38:02, 41:11, 1:17:12, 1:17:19, 1:27:27)
Secret: 5x (22:54, 22:56, 1:05:47, 1:23:50, 1:34:56)
Surely: 5x (24:15, 46:50, 47:56, 1:30:18, 2:15:14)
I Have no Clue: 4x (52:09, 52:12, 52:31, 1:39:05)
Whoopsie: 4x (14:50, 26:25, 32:01, 1:33:28)
Progress: 4x (41:59, 1:24:31, 1:39:35, 1:50:55)
Bother: 3x (50:52, 1:46:37, 2:09:07)
By Sudoku: 3x (1:20:43, 1:42:16, 2:03:53)
Clever: 2x (01:06, 10:58)
Lovely: 2x (11:36, 16:43)
Fascinating: 2x (01:40, 21:32)
Ridiculous: 2x (07:39, 07:42)
Going Mad: 2x (2:11:02, 2:11:13)
Magnificent: 2x (2:17:55, 2:17:57)
Useless: 1x (1:52:23)
Goodness: 1x (10:56)
Apologies: 1x (08:10)
Out of Nowhere: 1x (1:44:16)
Stuck: 1x (51:30)
Horrible Feeling: 1x (2:16:30)
Off to the Races: 1x (1:22:58)
Brilliant: 1x (01:15)
Break the Puzzle: 1x (1:13:29)
Extraordinary: 1x (2:16:18)
Elegant: 1x (2:16:40)
Gorgeous: 1x (16:02)
Approachable: 1x (03:16)
Bizarre: 1x (2:04:58)
Masterpiece: 1x (2:16:58)
Flurry of Activity: 1x (52:18)
Think Harder: 1x (2:05:31)
I've Got It!: 1x (1:17:09)
Snake: 1x (49:26)

Most popular number(>9), digit and colour this video:
Fifteen (24 mentions)
One (177 mentions)
Red (4 mentions)

Antithesis Battles:
Low (2) - High (1)
Even (26) - Odd (5)

FAQ:
Q1: You missed something!
A1: That could very well be the case! Human speech can be hard to understand for computers like me! Point out the ones that I missed and maybe I'll learn!

[korosei]

On the mistake at 47:18, where he forgot to disconnect R7C1 from R6C1. Here's a one solution:

If R6C1 does not connect to R7C1, it is important to note that the line extending upwards from the bottom left most dot will only be 2 cells long and cannot sum to 9 in two cells because it see 1, 7, 3 and 4, and cannot sum to be 15 or more because they see 7 and 9.

Now consider the line extending to the right, it has the options of joining to the 3 in R8C2, joining to the 6 in R8C5, and extending further. All of these options fail.

Extending further means it'll be at least length 5 (min sum 15) but the upwards path sees 7 and 9, and thus cannot be only two cell long.

Joining to the 6 forces the dot in R8C2 to be in a corner and must turn up. But R7C1 doesn't join R6C1, so it must run right, forcing a closed loop.

Joining to the 3 forces a 9 into R9C2, see pencil markers. However, the two cell path cannot sum to 9 as they see it see 1, 7, 3 and 4 in the column.

Thus, R7C1 must join to R6C1, QED.

[johannapy]

These long videos are amazing to help with falling asleep.

Honestly, I love watching CTC videos during daytime but it's also now part of my nighttime routine when my insomnia makes me suffer. Simons voice helps me feel comfortable and I get distracted from the internal dialog anxiety is having in my head by trying to follow the logic.
Plus I get so happy when I can find any deduction by myself no matter how small.
I'm just so grateful for the content...

[mmolina]

1:07:46 You’re not just ‘some nerd’ making 2 hour videos solving sudoku puzzles…you’re the king of nerds! Our king. All hail Simon, long live the king!

[douglasdunkle]

The software should allow a second color for the lines. That way you can distinguish between actual lines and hypothetical ones.

[peterhoare]

as my daughter put it apologising for the length of these videos is like putting on a star wars marathon at the cinema and then apologising for how long it is. i watch these videos because not only do you mange to solve them but you manage to explain the logic on the way making it feel like i can understand something when I wouldn't have a clue where to start

[wrmblood]

Please don't stop the ludicrously long videos, I think I speak for everyone when I say we (Mark too, probably) love watching you suffer!

In all honesty though, the super long videos are a pleasure to watch.

[nairit]

me, after solving this in 10 hours : I'M SO PROUD OF MYSELF

[Wecoc]

We're starting to get into 'The Lord of the Rings movie length' territory (and I'm okay with it)

[curtiseichner]

You should definitely do an escape room in real life at some point!

Another recommendation is "Understand". It's a puzzle game where you must intentionally pass or fail a series of puzzles in order to understand the untold rules of each puzzle. Sometimes you must go back to prior puzzles to hone your understanding. It's a fantastic game.

[concofps]

2:05:00 - To be able to construct a puzzle where two options such as this are still available THAT far into a solve in absolutely incredible
Also, I do wish ppl would read the comments existing before posting something which has already been said. Simon doesn't need 100 ppl telling him he forgot to delete one line in a 2 hours long puzzle.

[dzaijn]

Unbelievable. I've been soaking in everything I can from this channel and my brain feels healthy for the first time in at least 3 years. You are amazing, Mark is amazing, everyone surrounding you are amazing and I love every minute of every video (the longer the better) you most graciously share with us. Thank you Simon.

[deathsleet]

I love how at 2:02:25 he comments that a negative constraint could have resolved the 58 pair in box 7 and that is exactly the case…the top one had to be 8 since 9+5=14 and 8+6=14. So, the same spot he noted didn’t have a dot to eliminate the 2 also resolves the order of remaining digits

[livedandletdie]

I see, Simon did a logical leap in this puzzle, not as great a logical leap though as to think the viewers doesn't enjoy hours upon hours of mind numbing sudoku solving, the longer the videos the better. Because we find not only the solving interesting, but having some sound in the background, is comforting, and in these trying times, hearing a familiar voice for so long is pretty comfortable. Let alone entertaining with all of your simarkisms as the community has called it.

People on Youtube have always enjoyed the longer format videos, I used to watch 6-7 hour videos on here when I was unemployed, even if I missed 5-6 minutes of the videos it didn't matter, and if you thought sudoku is nerdy, then you don't understand how watching grand strategy games being played for a minimum of 6 hours per video is the nerdiest thing I've done in life, watching someone play Warhammer 40K with several players and unlimited army sizes, or watching someone in a video game do extreme challenges that require more patience than sifting for uranium atoms in seawater.
2 Hours is child's play Simon, it's 2 hours of enjoyable child's play. Not to say we don't love the usual 30 minute videos, but it's still lovely when we get the Sudoku movies, because it really shows off how passionate you and Mark are about Sudoku and similar puzzles.

[imistborn]

My wife and I found your channel not long ago, and we LOVE to watch your longer videos. Our nightly routine has become climbing in bed and watching one of the longer Sudoku videos, to which we typically fall asleep. We both highly enjoy the logic process Simon goes through, but it's absolutely true to say your videos have a very relaxing and cathartic effect. We sincerely appreciate you guys running this channel!