The Almost Perfect Sudoku

Normal sudoku rules apply. Within each row, column and box is one 'marker' cell. Marker cells must contain all digits EXCEPT 6. The row for each marker cell is indicated in row 1 of the grid. For example, if r1c2 = 9 then r9c2 is a marker. The column for each marker cell is indicated in column 1 of the grid. For example, if r3c1 = 7 then r3c7 is a marker. The position for each marker cell within a box is indicated in the lower-right corner of the box (position 9). For example, if r3c3 (lower-right for box 1) = 2, then r1c2 is a marker. Black Kropki dots in the grid indicate adjacent cells in the ratio of 2:1 (one cell is twice the other). ALL black dots are shown.

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▶Credits◀
Music: Tim McCaskey (Guitar) or Lucy Audrin (Piano) or Riffclown plays Mozart's Sonata no 16 ("Sonata Facile"), and Mark’s outro music by Riffclown.
SOFTWARE: Thanks to Sam Cappleman-Lynes and Sven Neumann
Logo: Melvyn Mainini
Opening Credits: Joel Blundell

▶ABOUT US◀
Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the twelve-time winner of The Times championship and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.

Thank you for watching!
Simon and Mark

▶ Contents ◀
0:00 Theme Music & News around the channel
2:36 Rules of today’s puzzle
6:21 Start Of Solve - Let's Get Cracking!

[Silent_Sounds]

that puzzle was gorgeous. I'm amazed at your ability to solve it so quickly, and I'm even more amazed by the person who was able to make it. Fabulous and inspiring. Happy birthday, Josh. I wish you nothing but the best.

[goleyeath]

This was a neat puzzle to solve. Props to NotThatItMatters for coming up with a version of this ruleset that doesn't just allow you to write a 1 in r1c1!

[emilywilliams]

Your grasp of this (for me) complicated indexing scheme was impressive, Mark. Again, I felt as if I was following you right along, totally understood everything - and then I downloaded the puzzle in order to solve it myself and got all confused almost immediately. Thanks for this video and for solving this puzzle in honor of that young man's birthday, I hope that Josh will have minimal suffering during his treatment and go on to live decades longer cancer-free once it is over. Thanks, as always, for making CtC such a great community.

[stangerrits]

I really like it when the two puzzles on a day relate to each other in terms of ruleset or solving technique. Really feels like you actually learn something since things you’ve get explained in the first solve you watch, come into practice in the second one.

[raysouth]

I love what’s happening with 3 in the corner, not just party sparkles, but congrats in the end popup box. Way to go Sven!

[trisha]

Hope you had a great birthday Josh and hope you recover soon. Sending my love and prayers to you and your family

[piarittersporn]

It's always amazing how quickly Mark finds the first step to a solution. I needed a little support again at the beginning (box 1), but after that I was able to continue on my own. A great puzzle.

[dashiellv]

65 minutes. It felt straight forward, going through the constraints and wittling down the candidates. Shading those cells that can't be markers did help.

[cathybryant]

So funny to have 2 indexing puzzles today. I did this in 20 minutes - years of computer programming help a lot! I did find that colouring cells that could not be markers was quite helpful. There are groups of cells that can be immediately eliminated as markers, which meant that once I found the first marker the rest of them came almost immediately (except for one x-wing of markers that took a bit longer).

[johnpauladamovsky]

18:09 - *PENCIL FEST* - That sounds like a really fun party to attend for the owners of heirloom-quality luxury mechanical pencils. I own a Modern Fuel Titanium pencil, machined from a solid piece of Aerospace-Grade pure Titanium, it's a great status symbol.

[Coyotek]

27:41 ... I had a similar feeling as Mark, going from 'How the heck do I start this' to 'Oh, I'm done then' in far less time than I expected

Nice puzzle!

[MrMouski]

Superb setting. Loved it all the way through. Simply brilliant.

[Scott]

Josh - Happy birthday- John Donne tells us 'No man is an island' - best wishes.

[Laezar]

I got stuck for a very long time cause I wasn't sure if "marker cells contain all digits except 6" meant "must contain" or "may contain". I just decided to take a leap of faith at some point and assume it meant "must" cause I had no clue how to advance otherwise, I feel like that could have been worded better cause the puzzle is a lot easier with that rule (since as soon as you get a double in marker cells you can eliminate all cells from a marker cells from other cells, and considering you get a double very fast it probably makes everything else way easier).

[Wolves]

Mark: "let me colour these yellow"
Me: "sure, go ahead"

[Swisswavey]

These puzzles are an awful lot easier if you remember the rules! Lovely puzzle, thanks for sharing it.

[gregdyck]

Actually, I believe he was an hour early! Can't expect perfection given the puzzle name.

[Paolo_De_Leva]

Thanks for the chapters.
I remind all viewers that we can skip chapters forwards and backwards by pressing
_<Ctrl> + <right/left arrow>_ on a Windows PC
or
_<Option> + <right/left arrow>_ on a Mac-OS PC.

[johnpauladamovsky]

26:07 - "NOW, Come on, more marking, more fun, more speed, *MORE POWER*..." - Power for the sake of Power...!

[karremania]

I was well over 90 minutes untill it 'clicked', absolute amazing, i spent a fair good hour mostly 'HOW WHY WHEN BUT?', the absolute joy when suddenly stuff becomes to 'click' together, the contrain on the black dot, the markers, i cant remember a recent puzzle that gave me so must amazement and joy to suddenly wrap up. My hardest bit was Mark's initial statement, each marker contains 2 same digit's and no number 6. In my mind i could have been all 7's in the markers.