It's funny... I can follow every step you take. I understand the logic. But I'm pretty sure I couldn't find an empty rectangle in the wild to save my life.

I'm so ashamed to say that when I clicked on this video and saw that it was a classic sudoku I figured I would give it a go. It then took me over two and a half hours to solve. Watching you breeze through it without any difficulty at any point makes me at once frustrated and in awe. Great job!

The lessons on locked pairs and empty rectangle at 5:32 and 14:10 are extremely helpful

He's driving me crazy when he ignores one empty cell in a square to go off looking for different numbers.

I like to think im good at sudokus, but when i hear him discuss how he figured out how there was no six at around 6:50 , that really shows how much more there is to learn!

9:44 thought my laptop crashed.

I had the whole grid filled out with candidates, but without the empty rectangle insight there was no way to unwind the pair/triple/quad cycles. Spent far too long staring before I watched you crack it!

The first example of the anti rectangle didn’t make sense to me. Then the second did make sense. I went back to the first example and now I understand. Thank you!

So, until given a puzzle book 6 weeks ago, i tried Sodoku twice. After watching 5 of these videos today, i realized you cannot do this game without pencil marks; which is how i solve many other puzzles. I tried them in pen over the last 2 weeks, and now i have 4 inked, indecipherable, works of art. Thank you for this channel. It's my new favorite. Cheers

He thought that he'd solved all of the 6s at 13:25, but he didn't recognize his oversight until 16:16. Thanks for illustrating the rectangle technique.

Empty rectangle! Never knew there was a name for this. I always thought of this as trying out all possibilities and checking if they all lead to the same elimination. Literally the very last trick I ever use as I had no method to spot them. Love the column/row trick! Subscribed

4:18 all I was missing to complete the solve. Really wish I had seen that earlier. Thank you!

The empty rectangle has come up as a hint so many times in the app I use, and I've never understood it. Thank-you for clearing it up for me.

Always a pleasure watching your Sudoku solves Simon, I didn't know about empty rectangles so thank you for the explanation.

5:00-6:25 When he mentions the empty rectangle, by deducing that 6 is not possible on the cell he marked '2' in the corner, if you fill in some of the more obvious numbers, you can quickly deduce the number in that cell is actually 8. Using that 8, you can then solve the upper square to be 2, then most of the 3x3 square in the top right hand corner can be solved. Great piece of logic there

5:00 - Empty Rectangle Pattern

The 7 in the bottom right corner could have been found much earlier and would've had other implications for the grid.

I paused it at the beginning to try it, messed it up twice, watched until you described the empty rectangle, and that finished it for me. I used it to resolve the exact same two unknowns that you did. Very cool!

For the first time, I tried this puzzle before watching the video. I think that the "empty rectangle" made the difference between me getting thoroughly stumped and having to guess at a point, and solving it properly. After my first guess led to duplicates after going throughout the grid, I *tried* to find out how two colors could be put in the same box. That would have helped, I think.

So this is what Sean Lock does in between episodes of 8 out of 10 cats

The "empty rectangle" method is fantastic! I've seen you use it in other sudoku puzzles and I've been able to use it, though I find it hard to see when the opportunity arises . I never write small numbers in because I prefer to remember what numbers pair up in which boxes, and if I think the puzzle is taking to long a time then I imagine one of the pairs as resolved and then think about how to resolve all the other pairs based on the imagined resolve... it's a great mental exercise. Thank you so much for teaching the 'empty triangle' technique.

"Today might be kind of a long video." Hearing this comment during a 17-minute video, just a couple of days after watching the 1 hour 40 minute video, is very funny. It's amazing to me how far sudoku, and this channel, and - I imagine - a whole lot of viewers like me have come in the past year and a half. One tiny silver lining to the pandemic cloud.

Just getting into your videos - never heard of empty rectangle before this one. Wicked.

I love CTC's solving style so much I made a video on my channel where I analyze each step of this solve. In addition to explaining the strategies used, I add a couple of pause the video moments and some alternate solving paths, similar to how someone analyzes a chess game.

wow, I FINALLY understand how the empty rectangle works! could never wrap my head around it until this video

Came here from your "The Witness"-series and this was my first finished sudoku and first sudoku video... it took me 3 solid hours making an effort not to guess anything, very eye opening to see an efficient method afterwards.

15:22 was what I needed to solve this. Thank you!

Amazing to see how much more comfortable and polished your videos have gotten over the past year or so. This is fine but definitely not as easy to watch as the newer stuff.

Thanks you,,, finally I understand the logic of the Empty Rectangle, And I did spot the 2nd one :) :) (after you pointed out there is one) Making some progress :)

I started solving it myself then got stuck ! then I watched you use the magic technique ! wow

I was always so confused about how to spot empty rectangles, but knowing they follow similar patterns as x-wings has really helped!

You are so fast and accurate, impressive! These are the best sudoku videos around. One remark though on the way you explain the empty rectangle: you talk about it as if there can be more 6's in the same 3×3 block, which I found confusing at first. Why not just use the singular, 'The 6 is either in this row, or in that column, (or both), ...' ?

The ones where you demystify some logic i was struggling with seeing are my favorites.

44:22. Made a leap of faith based on rules I learnt off here - I wasn't quite sure if I was doing the right thing, but it worked! Perhaps it does go in when I drift off to sleep! Keep it up!

No clue about that empty rectangle when solving it by myself...took me several X-Wings and Skyscrapers (also made progress there due to your videos) to finally crack it after endless time by excluding several numbers...such a complicated pathway compared to the shown solution...Big thanks for showing that route!

Lol, so I was just stuck on a puzzle for several hours. After not making any progress for an hour, I give up and decide to watch some cracking the cryptic to get some inspiration. This is the first video I watch, and I realize I might have an empty rectangle that I missed. Go back to my puzzle, find an empty rectangle in a couple minutes. Three minutes later the entire puzzle is solved! Thanks!

The amount of progress in this channel has been phenomenal.

Great explanation of the empty rectangle. I think I've got it now. Thanks.

15:20 that literally solved it for me, i was stuck for so long and couldn't figure out why. but the simple fact that the center square isnt a 9 just made everything domino effect into place for me. those empty rectangles are so powerful wow

Empty rectangle really screwed me up till late in the game. So well done for spotting it so early.

Good! The empty rectangles trick was new to me, and even after 2 hours I couldn't spot any other way to solve this one. Wonder how often it's the key move.

I did the sudoku first, then when I couldn't continue, I went back to the video and you helped me with the 5/6 pair. I went on with the sudoku, when I needed help again I continued the video and you taught me the empty rectangle trick with the 5/6 pair. I continued, nearly solved the whole thing, had a bunch of 1/2/9 situations that I could not fill in. I remembered the empty rectangle with the horizontal and vertical perspectives, identified a field that in any case could only be a 1, solved the puzzle! Thank you!

Thanks, I think this tactic will help me in future solving!

Thank you for the tip! I’ve been stuck on a few hard sudokus for a week, hope this helps

I tried it on my own took twice as long as you, but i found the key was triplets - there were so many and cracked the puzzle for me!

Empty rectangle. I think that's all I'm missing in my life. Thank you!

I'm pretty sure this will revolutionise my Sudoku game. Thank you!

I'll need to remember the empty rectangles technique, thank you for showing this!

Another quick and easy one from last year. I did this one in only 22 minutes, so only 5 minutes more than your solve (but I wasn't explaining anything either). Thanks for the videos! Also I like your explanation of the empty rectangle a lot better than some of the descriptions online. Even though your explanation didn't define why it is called an empty rectangle (the number you are looking at can't be in the other four (or more) cells in the box, those being the empty rectangle as I understand it) your description does identify the more salient point that the row and column lines formed next to the empty rectangle combined with an interlocking pair does let you eliminate the digit from the square seen by the other cell on the pair in the matching column (or row if the pair is in a row). See, even I have trouble explaining it, but at least I do understand it well, now.

42 MIn on my second go but I did not use the empty rectangle technique. it's always a pleasure to see you cracking! hope to see you again!

I had no idea other people used this technique! I have been playing sudoku for 4 years now and have only known this method and taught myself everything I know. My record time on easy is 1:09 and 8:47 for Expert. As I finally look at stuff online I realize I know pretty much everything and love watching this youtuber now to see the crazy puzzles he gets to do- ill pause it and try to beat his time! I beat him for this puzzle and most because he stops to explain things as I go on.

Love the trill in Mozart’s Sonata in C major! (Love your videos too...)

Very neat at before the 4:50 mark seeing that quickly on the boxes to the far left that the center column had 2 squares in need of a 5 and 6. He'd be a good chess player at tracking loose and hanging pieces.

14:05 X-wing on 1's in R1C3 & R1C5 & R7C3 & R7C5 eliminates 1's in R8C3 and R8C5.

`I spotted the empty rectangle for 5s and 6s but proceeded with the 5s....your explanation that the 5 in R9C1 and so we must go for the 6s is the eye opener!!! I dint go for the empty rectangle and got lot more numbers in various squares but there were so many 6s in the unfinished puzzle, that I went for the solution done by you!! Good show

Thanks, always learning. Just a note that the check button says it doesn’t look right even when all is correct. This was the 1st time I’d tried it out. Thanks again.

“This it’s gonna be a long video” four years later we have over two-hour videos and these ones look like a breeze Kudos CTC!

Around 4:39 I think the correct move should be focusing on column 2 and realizing that 3 has to be in r9c2, and this will certainly avoid using the rectangle technique for box 6, which could be a bit unclear

0:51 I love how Simon refers to 17 minutes and change as a long video when people nowadays complain that the puzzle is too easy if the video is that short! How times have changed...

To me, a novice, it appears that initial “empty rectangle” of his with the 6 unlocked most everything... and that the puzzle was meant to be much, much more difficult if you didn’t know the technique. Gosh I adore this channel.

He is much better at explaining for the masses! I just do it all in my head, without leaving the little numbers behind, which are so important for teaching people how to improve their skills.

7 in the bottom right corner . I saw it earlier . I think that would make the puzzle easier further

I sort of learned a new trick, the empty rectangle... but I doubt if I can recognize when to use it and when it can't work. But I imagine it's something I'll be able to learn now that I've seen it. I guess I'll have to keep watching! great show, thanks

Awesome technique! Thanks for showing it

I didn't know about this trick. Thank you.

The way I internalized empty rectangles is when I have a pair and a 3x3 with only a row and a column, together they point at a location. If a number from the pair is in that location, it messes up where it can go in the 3x3 (Its similar to proof by contradiction: If its here, then it leads to a problem, so it cant be there)

By George I've got it! No more 'what if' guesswork? Well perhaps....... Cheers, Stewart

I prefer when you click on a cell and it highlights the corresponding column/row/block. Makes it easier to see.

59:05, while listening to a podcast. did plenty of staring blankly at it waiting for my brain to notice any kind of pattern. embarrassingly resorted to entering all the possibilities for every cell, and it was only then that i noticed a triad in column 3 that ultimately unwound the rest of it for me.

This puzzle took a little under 2 hours!! For me, I had to look where things couldn't be by a little guess and check. Going to watch video now and see if there was an easier strategy!! Thanks!

This randomly showed up in my youtube recommendations, so a bit of a necro. The most advanced techniques needed to solve the puzzle are a Sashimi X-Wing and a BUG+1 (or short chain) Singles: r6c6=5, r6c4=6, r6c2=8, r6c3=4, r6c9=1, r3c7=4, r7c1=4, r9c5=4, r1c4=4 c2 has a naked pair, 7 & 9, in r1c2 & r7c2. r3c279, r5c279, & r9c279 Singles: r9c2=3, r8c9=3, r5c8=3, r9c8=1, r2c7=1, r1c8=2 r23c6 form locked candidates for digit 2. r23c452 r1c23 form locked candidates for digit 7. r3c137 Singles: r9c6=7, r3c4=7, r7c9=7, r1c2=7, r7c2=9, r9c7=9 X-wing for digit 1, r3c1, r3c6, r8c1, r8c6. r38c351 Singles: r3c3=3, r2c4=3 r23c5 are locked candidates for digit 5. r78c55 r2c1, r2c9, r4c1, r4c8 together form a Sashimi X-wing for digit 6. r3c86 Singles: r3c8=8, r2c5=8, r5c9=8, r3c5=5, r2c3=5, r5c2=5, r3c8=5, r3c2=6, r5c7=6, r7c8=6, r2c9=6, r4c1=6, r8c5=6, r3c9=9 r23c1 form locked candidates on digit 2. r1c52 There's an obvious BUG+1. But I like chains, so r5c5=9 => r4c49 & r1c59 => r1c3=9 & r4c3=9, which is a contradiction, so r5c59, r1c39, & r4c39. Singles: r1c3=1, r3c6=1, r7c5=1, r1c8=1, r3c1=2, r2c6=2, r4c3=2, r5c5=2, r6c6=2, r7c7=5, r8c4=5, r5c1=7, r8c3=7, r7c3=8, r8c7=8, r1c5=9, r2c1=9, r4c4=9, r5c3=9, r8c6=9

Every time I got stuck on this one it was an obvious pencil mark I was overlooking for a naked single or the second empty square. I learned the empty square working through this video. Maybe now I can get through the first puzzle on Sven's Sudoku Pad... I've only been going at it for 2-3 days lol

The way you make us understand is great. Thankyou sir

This video did the trick. I tried the puzzle before watching, and I got stuck. I saw your description of the empty rectangle and I paused the video and was able to finish the puzzle by spotting the second empty rectangle on my own. So, I picked up a skill. I really think the second empty rectangle technique was necessary.

The technique I learned from this was a number in two columns "squeezed" the number in the bottom row, which I never thought about before, hopefully will use it later on.

When you still fail the exam 5 minutes after the teacher finishes explaining the concept ... smh "Now I wonder if you've seen it." Bruhhh, you have too much faith in my abilities.

You are teaching me one thing: Don't get so engrossed in the logic that you forget the obvious.

making heavy weather of the 5/6 look straight to the 3s

I was waiting for you to put the 7 in the bottom right box at 8:55. I think that would’ve unlocked things much earlier, especially in column 2

I was stuck on puzzle #23 in your app. Even with hint #2 about this technique for the 7s and 9s, I just couldn't wrap my head around this. This video is very helpful - I wanted to understand it before using the hint and continuing.

Trying to do this on my own, I got stuck specifically because I didn't know the empty rectangle for the 6; as soon as it was mentioned, I pressed pause and could finish the puzzle, using the 9 one later on. In other words, this specific puzzle was an excellent lesson on that technique, and would have been very difficult without it.

Now that was a sudoku class for me. I've been here for over an hour trying to get my tiny brain to absorb it all

Genius. how does he spot these so quickly.

I like this technique demonstrations here, going more or less deeply into a single one, like in this case, the empty rectangle, and the previous one with the X-wings. I'm still hoping for a nice BUG solve some day. ;)

As a beginner I appreciate this video. I have not seen another video describing it.

I learned something, thank you! Was able to put it into practice for once. haha

That's a new one for me. I think I understand it. I'll put it in the tool box and give it a go. Thanks for the tip.

That's a really interesting technique. I'd got to a point where it looked as though there could be two solutions (I know that's impossible), only this technique sorted it out. Thanks for that.

I was banging my head saying 7 in the bottom right after he filled the one under it for like 4 mins I think but the technique you showed off I never new about so that was helpful

I got to a point on this grid where all the empty squares each had 2 possibilities and I couldn't see where I could crack through it. I tried a trick where I used the colors to represent the numbers to make a guess on one of my squares and followed that until I got to the end, or got a conflict. I got lucky as that first guess didn't conflict anywhere. So just replaced the colors with the corresponding numbers, and the check button called it good. Using the colors allows me to keep my marks in the grid so I don't lose track of what point I would need to use the back button up to.

Before watching your channel and sudoku guy I hardly ever finished expert sudoku, now my best time is 8 minutes.

Hi Simon thanks a lot I learn so many technique from you . Now I can solve many hard sudoku problem. Btw i am from the Philippines.

Thanks for the video. I can see the patterns in things that are present; my problem is seeing the patterns in things that are not present! Anything 'hidden' just chews up time for me, but I get them eventually. Maybe I need to improve my notation skills.

After listening to your empty-box analysis I wondered why the 6s couldn't be on a diagonal from one another rather than just vertical or horizontal. This is similar to the 29 diagonal pair in the middle box.

Nice teaching moment, keep it up. I might be able to get through one of these without your help.

Simon so when I am playing I look for singleton's first.

took me 40 minutes to realize I seriously screwed up, started over, and then another 44 minutes to solve it. Very nice puzzle.

The most used sudoku Technique: look up the answer in the back of the book...

is there a good ie quick way of spotting hidden triples, when other numbers are also present in those cells? Often takes me ages to see them?

27.58 I'm trying to train myself to start seeing Empty Rectangles. I had to restart twice due to pencil mark errors, but I don't think I memorized any numbers, only remembered some logic that I should know anyway. So my solve, with a couple of asterisks, was.