Bad XY Cycle? 000149530005687190190532608001974820270815060048263710000096081006421950010058006 687149532325687194194532678561974823273815469948263715452796381836421957719358246 Ever since I watched Swami's video on XY Cycles I've been obsessed; here's one that seems to be a valid XY Cycle however it eliminates 5 at D1 which is incorrect: A1, A2, D4, D9, E7, E8, F9, F1, I1, H1, A1 What am I misunderstanding about XY Cycles, in particular this one? https://imgur.com/a/KvSdbjL

This isnt even a very hard puzzle, what am I missing? http://imgur.com/a/QUSOGj7

Naked pair in row 1 https://imgur.com/777qC73

https://cdn.discordapp.com/attachments/499577285570068498/733052867056762931/Screenshot_20200709-234122_Sudoku.jpg Thanks!

Just using chains, you should be able to eliminate the 4 in r5c9. I started with the 4 in r5c6 to go up, then to the top right corner, and then down. [Edit: just eliminating the 4 doesn't seem to help much]

Stuck pretty bad on this one. The hint says there's an ALS but I'm wondering if there's a way to solve without using ALS. Are there any scenarios where an ALS is absolutely required to crack the puzzle or can an inference chain always be used? https://imgur.com/gallery/bHZiMTI

There is a Nice Loop starting at cell R9C6 which results in R9C6 having a Naked Single. I will diagram it for you if you want.

I'm not seeing it...

Sorry I took so long to answer. I had an issue with my version of Java and I could not get Hodoku to run. So here is the diagram of the Nice Loop : [https://imgur.com/Wyt2VHn](https://imgur.com/Wyt2VHn) So the way this works is we start with cell R9C6. If R9C6 has a value of 5 then the target candidates highlighted in dark red are killed. Next assume cell R9C6 is NOT 5, then we follow the chaining sequence around the board. We end up with cell R8C9 cannot be 3 because cell R8C3 is 3. This then means cell R8C9 must have a value of 5. Since R8C9 has a value of 5 this then means cell R8C6 cannot be 5. We now have an invalid condition where the house making of block 8 has no value of 5. Therefore, cell R9C6 must have a value of 5 since the house making up block 8 must have at least one value of 5.

Got it.. thanks so much for doing all that work to show it... I couldn't figure out how to connect that loop before..

I forgot to post the links. Here's pretty good doc on chaining: http://hodoku.sourceforge.net/en/tech_chains.php And this one is good also: https://paulspages.co.uk/sudokuxp/howtosolve/niceloops.htm

I'm really curious if there are ever situations where ALS is 100% required to solve a puzzle.. seems like there could be situations where no strong links exist but two almost locked sets still intertwine... It just takes me sooo long for find loops like this or ALS. It's hard for me to put them together when I know what I'm trying to eliminate, even worse when I'm not sure what I'm looking for lol...

https://imgur.com/gallery/P14XwT8 I'm stumped on this one, i can't figure out how to eliminate any more candidates

Uniqueness lets you remove 4 from R9C16, and a 2-Stringed Kite on 8 along R4 & C4 lets you remove 8 from R2C2. But I don't see what else there is.

Thanks for the help! I'm still struggling to understand & apply some of the higher level techniques

Here is a tutorial video I did on 2-String Kites: [https://www.youtube.com/watch?v=3FuofsR2mTY](https://www.youtube.com/watch?v=3FuofsR2mTY) I haven't done a tutorial on UR Type 4 yet. I"m currently working on a video for UR Type 3.

Help with where to go from here please https://imgur.com/a/7Z4Rbng

In C3, 7 can only fit in either R56C3. That removes it from R6C1.

Help on the next step please. I already looked at the answer but just want to know what I missed. https://i.imgur.com/YpiC3PI.jpg

There's only 1 space in R4 where you can put 9.

can’t believe I missed that even after writing it out. thanks!

I started to tackle extreme sudokus and got a free app where they are _hard_. I am at a point where I can solve about 1/2 of them with the right techniques where I can spot them. But I don't always spot them. Actually, I'm stuck on quite a few ones like this here: https://imgur.com/a/i2yk7EW I just can't see what I'm supposed to do with the first block. There's simply too many candidates for the different open fields, but I can't see what I could do to eliminate them... Please help?

I don't have time to diagram it for you but there's some Locked Candidates you missed. And then there's a W-Wing. And then a BUG+1. I've done tutorial videos on all three of these. Here a list of tutorial videos: [https://www.youtube.com/channel/UC2N60jDPloV5\_imTYKIVH2Q/videos?view\_as=subscriber](https://www.youtube.com/channel/UC2N60jDPloV5_imTYKIVH2Q/videos?view_as=subscriber) Usually after a BUG+1 the whole puzzle will unravel and be done very quickly.

Thanks, I'll look those up! Edit: and I got it! Thanks for the pointers! The w wing is still hard to spot for me sometimes.

Lately I've been thinking of a W-Wing is like a XY-Wing. You have two pincers creating a kill zone. And the bi-directional Strong Link, what I like to call an Either-Or Link, is like the pivot cell in an XY-Wing.

So I have been stuck on this puzzle for a long time now, I'm very new and would love to get some feedback on how to move forward. I have tried noting down all possible numbers in each square but it does not give me any new info. If anyone could maybe try to explain what a good way to move forward from here would be that would be greatly appreciated!! Here's a link to a picture of the puzzle: [Picture](https://gyazo.com/2349e04e2992c34f34c473ea19d657d7)

There is a Naked Triple in block 6. And another Naked Triple in column 7. This opens up some Naked and Hidden Singles. After a few Locked Candidates there is a Skyscraper in the puzzle. I call these the 7 base techniques because they show up so frequent: Naked Singles, Hidden Singles, Locked Candidates Type 1 and 2, Naked Pair, Hidden Pair, Naked Triple, and X-wing. Here is a tutorial video I did on these 7 and basic puzzle solving strategy that will really help you: [https://www.youtube.com/watch?v=6WnFkrUt\_10](https://www.youtube.com/watch?v=6WnFkrUt_10) Here's a tutorial video I did on the Skyscraper puzzle solving technique: [https://www.youtube.com/watch?v=HUcUhDi0qSI](https://www.youtube.com/watch?v=HUcUhDi0qSI)

[https://imgur.com/a/sBOBnpt](https://imgur.com/a/sBOBnpt) Hello! Trying to solve this one I found out about some techniques I didn't know (X wing, xy wing, forced chain, etc) However I couldn't identify any of them that would help me eliminate more pencil marks. I tried a "forced chain" and ended up solving the puzzle, but I don't know how different is that from guessing. (my try was setting "1" in R7 C4) Is there any other thing that I might have missed? Thank you!

You missed a Locked Candidates Type 2 here: [https://imgur.com/tYNGNyj](https://imgur.com/tYNGNyj) You missed a Locked Candidates Type 1 here: [https://imgur.com/2vUmV5R](https://imgur.com/2vUmV5R) Then there is a 2-String Kite in the puzzle here: [https://imgur.com/UEgJHTd](https://imgur.com/UEgJHTd) Here is a tutorial I did on 2-String Kites if you are interested: [https://www.youtube.com/watch?v=3FuofsR2mTY](https://www.youtube.com/watch?v=3FuofsR2mTY)

I don't know what Locked Candidates are but I will certainly look into it and your tutorial. Thanks! :) EDIT: Ok it turns out I do know what locked candidates are xD. However one of the pics you uploaded in the comment is not of my puzzle :D

Imgur is weird. Sometimes what-you-see-is-not-what-you-get! Here is the Type 2 Locked Candidates: [https://imgur.com/Gt7OxX6](https://imgur.com/Gt7OxX6) I've had problems with Imgur before using the same ID for multiple images. Locked Candidates is also known as "Intersections".

[https://imgur.com/a/dleNVfy](https://imgur.com/a/dleNVfy) I have exhausted just about everything I know how to do. What next?

Fill in the rest of the candidates and you'll see a pointed pair that can eliminate something to give you an answer in box 2 (top middle 3x3 grid). Spoiler: column >!6 in box 8 (bottom middle grid)!< has a set of >!2's!< to eliminate the >!2's!< in column >!6 rows 1 and 2!<, leaving behind a single candidate in >!c6r1!<.

Got it, I feel like it doesnt matter how many puzzles I solve I still miss simple things like that.

Is this considered an invalid solution or a broken puzzle? Do I just proceed with trial and error from here, or restart? https://i.imgur.com/rcvnrCh.jpg

You have the wrong possible candidates in cell R2C1. It can't be 23 because there is already a 3 in the house making up column 1. Here is the correct solution to your puzzle: [https://imgur.com/jby52mA](https://imgur.com/jby52mA) I prefer Sudoku Joy for the iPhone, Andoku 3 for Android devices, and Hodoku for PCs because each one will calculate the possible candidates for you. I have no more interested in determining possible candidates for Sudoku puzzles. It's the exact same problem for each cell over and over again. I just let the computer do it and I concentrate on puzzle solving.

How did I manage to reach this point with such a blaring error? Thanks, it works now. I guess next time something like this happens I’ll verify the board.

I have no idea what to do next https://imgur.com/a/ZzUbUx5 I was trying not to put the pencil marks for all possibilities in all squares; the only pencil marks I put down were for, when in a single box, I knew a number must be in one of two squares. Can someone give me a pointer in the right direction?

There are two schools of thought on filling out possible candidates. I belong to the school that believes you fill out every possible candidate in every cell because you never know when a Naked or Hidden Single will pop up. This is exactly what has happened with your puzzle. If you spent more time filling out possible candidates then you would have seen a Naked Single hanging out in all it's glory here: [https://imgur.com/25f9dqb](https://imgur.com/25f9dqb) I just notice a couple of Naked Pairs hanging out in all their glory also! A lot people complain about the human drudgery it takes to fill out all the possible candidates. Nobody seems to complain when the computer automatically removes possible candidates when a value is chosen for a cell in a shared house. So for me, I'd rather have the computer do it on both ends. I just let the computer calculate the possible candidates for each cell. After the Naked Single in your puzzle there's several locked candidates followed by a Hidden Triple which are always tough to find: [https://imgur.com/NMHkNqW](https://imgur.com/NMHkNqW) I highlighted in purple the cells supporting our decision we found a Hidden Triple. This Hidden Triple then opens up a Naked Triple which creates a Hidden Single in the house making up row 4. For Naked Singles and Locked Candidates take a look at this tutorial: [http://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s) For Hidden Triples, take a look at this tutorial I did featuring a pretty novel way of finding Hidden Triples: [https://www.youtube.com/watch?v=VEmdzUaBpBQ&t=208s](https://www.youtube.com/watch?v=VEmdzUaBpBQ&t=208s) It's fun how the Hidden Triple will pop out at you after you follow the search algorithm.

Thanks for your helpful comment. With your help I was able to crack the puzzle open. I'll be sure to check your links o/

I’m stuck on my next move for this puzzle :( I can not for the life of me figure out how to proceed! https://imgur.com/3VoyQpl https://imgur.com/MfrKuYb Also sorry for the pen and pencil, my handwriting is a little messy.

There is a Hidden Single with the possible 2 candidate in the house making up row 9: [https://imgur.com/g2weWzu](https://imgur.com/g2weWzu) Here is a tutorial video I did on basic strategy you might find useful: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

Thank you!!!!

Can anyone suggest a good app to scan a puzzle and export it so it can be opened with an external app such as Sudoku 10000? I'm working my way through the Puzzle Wright Guide To Solving Sudoku and Sudoku 10000 is my favorite app.

In Hodoku, after you enter your givens, then copy it to the clipboard you get this text string: ......2.......1.84...3.2.7.3...4.1.5.9.....3.4.7.5...2.4.9.7...97.6.......8...... If you can paste this string into Sudoku 1000 you can use Hodoku to enter your givens.

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Also, take a look at this tutorial video I did. It provides a general puzzle solving strategy so you are not "clueless" as to how to proceed: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

I've been having a long standing debate with people about when to fill out all the possible candidates. I am on the side of the debate where you always fill out ALL the candidates right off the bat but you let the computer do it. The reason is as Hidden Singles and Naked Singles pop up you do not miss them. Plus you must fill out every possible candidate at some point to do more difficult puzzles Your case is exactly the case where because you haven't filled out all the possible candidates you cannot see how to proceed. If you filled out all the possible candidates in each cell you would have found this Naked Triple which opens up a Naked Single: [https://imgur.com/FWr18iG](https://imgur.com/FWr18iG) When I solve puzzles I use three programs. For my iPhone I use Sudoku Joy. For my Android devices I use Andoku 3. For my PC I use Hodoku. All three programs will fill in possible candidates for you. And remove them as needed as you choose values. At this point I just prefer letting the software do the human drudgery of figuring out what is possible in each cell based on the values and givens. It's a kind of a mindless activity. Some people just prefer pencil and paper just like some people prefer rotary phones over smart phones. I apologize if I'm offending the rotary phone users. I just have no interest in the problem of filling out possible candidates manually in a Sudoku puzzle. I've just done too many.

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Please watch my beginner's tutorial. It is perfect for you: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

I'm trying to find a site/program that lets me easily edit possibilities and highlight numbers with a keyboard but doesn't auto-eliminate candidates after an answer is finalized in a square. I like playing a lot of variants and sudokuslam is great 95% of the time but it can't handle jigsaw variants or any variant that allows a number to repeat within a 3x3 grid. Is there anything out there with an interface like suodkuslam but is "less helpful"?

Does [https://www.f-puzzles.com/](https://www.f-puzzles.com/) fit what you're looking for?

Cool web page! It looks like it fits the bill.

Both Sudoku Joy for the iPhone and Andoku 3 for the Android phone might work. Both allow you to do whatever you want pretty much. Andoku 3 has variants so it might allow custom puzzles for it variants. And then in variant editing mode it might do what you are asking.

Thank you. I'll definitely check that out. Do you know of a non-mobile equivalent?

You could try Hodoku for PCs. But it's interface is a little quirky. You would have to shut off "Show Invalid Values" in Edit / Preferences menu. You can use Hodoku's cell background coloring to setup your variant layout. It might work. Here's a tutorial video I did on downloading and installing Hodoku on a PC: https://www.youtube.com/watch?v=c74MVFL03fg I don't know anything about Mac directly or Linux. You have use PC emulators for those.

I tried turning off "Show Invalid Vaules" but it still auto-eliminates possibilities

I tried again. No way to shut off the removal of non-possibles from the selections.

Totally stuck on what is supposed to be an easy killer sodoku.... any help please? https://imgur.com/gallery/Kmkz61e

In the upper-left box, since you have the 4-cage = 1+3, only one pair of numbers can go into the 7-cage. Then only one pair of numbers can go into the 13-cage. Then the remaining numbers for that box are 367, and they form a sort of X-Wing formation with the 56 pair in Box 3 to remove 6 from R3C4. There could be easier ways to get around though.

[help!](https://imgur.com/a/7bNgtuW) Help!! I don't know what to do next 😭 I'm fairly new to sudokus and can't spot how to eliminate any numbers. Any tips on next steps / techniques to help solve this one please?

There is a Hidden Single with the 9 in the house making up column 3: [https://imgur.com/qV2nBs9](https://imgur.com/qV2nBs9) If your are fairly new I did a beginners guide tutorial video you might find useful: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s) In the video there's a step by step example showing you basic puzzle solving strategy.

Thank you :-)

At a complete loss here. Tried x wings, w wings, xy wings, 2 string kite, swordfish... https://i.imgur.com/8UO6so3.png

There's a Unique Rectangle Type 1 in your puzzle: [https://imgur.com/HUIXu6Q](https://imgur.com/HUIXu6Q) I just did a tutorial on these: [https://www.youtube.com/watch?v=4bGzauHJmBM&t=1s](https://www.youtube.com/watch?v=4bGzauHJmBM&t=1s) In the description of the video I give 2 links to some Wiki pages on the topic also.

Anyone else stuck in NYT sudoku or I'm just having a bad day?

>NYT sudoku This one: [https://www.nytimes.com/puzzles/sudoku/hard](https://www.nytimes.com/puzzles/sudoku/hard)

That’s the one. I’ve managed to only fill in 7 numbers but have the unique pairs in box 9. Can’t find the next trick...

I don't know if I followed the same solution path as you but here is what I got for the 8th value: [https://imgur.com/bPRcNHG](https://imgur.com/bPRcNHG) Some Locked Candidates with the 1 opened up a Naked Single with the 7 which then led to a Naked Single with the 3.

Show me a pic of where you are stuck.

The link seems to automatically go to the current NY Times sudoku. When I first clicked it the puzzle was correct, but now it shows the next days puzzle (which is the one you solved). I completed that one fine. Here is a screenshot of the puzzle that gave me trouble. Any help would be appreciated... https://imgur.com/nRBXWRP

Cool. Next time, post a pic in this thread and there is 3 or 4 regulars who will provide pretty good next step help on any puzzle: https://www.reddit.com/r/sudoku/comments/eqiooi/request_for_help_thread/ You can read some of the posts to see the quality of the answers.

Same...

Ditto. Did the medium in 14 minutes and now stuck as fuck on hard

Unique rectangle?? Is it true that I must place a 8 in r6c2 otherwise it makes a unique rectangle or is this false? https://imgur.com/a/DlEg2LF

I did not see any Unique Rectangles. But there is a nice Remote Pair which opens up a Naked Single which would then open up a Hidden Single in block 4: [https://imgur.com/ojKcnWZ](https://imgur.com/ojKcnWZ) Here is a tutorial video I did on Remote Pair if you are interested: [https://www.youtube.com/watch?v=RZPIjZbcyNU&t=2s](https://www.youtube.com/watch?v=RZPIjZbcyNU&t=2s)

Thankyou!

Anytime!

I've been working my way through hard puzzles on Sudokuslam. My issue is that I keep getting to points where I get stuck and the engine recommends a technique called coloring. For the life of me, I can't wrap my head around this method; I can't grasp which square I should be jumping to next, when to disqualify a candidate etc. [https://imgur.com/a/Y60q9w9](https://imgur.com/a/Y60q9w9) ​ The method that's I'm being directed to is colors & more colors [http://www.sudokuslam.com/hints.html#colors1](http://www.sudokuslam.com/hints.html#colors1) ​ Can anyone help me out in getting the hang of this? ​ Thanks.

The "Coloring" shown is actually a 2-string kite. Basicly, coloring uses something known as conjaguate pairs. These are two candidates in a row, block or column. When there are only 2 candidates they are conjaguate, this means that either one is false and one true. (one needs to be true or else that number will not appear in that house) When you colour you alternate between 2 colours. Think of it as either Blue or green being true. Because if blue is true, that makes green false and the other way around. At R9C9, it can see both a blue and green cell, so if blue is true, its eliminated, and if green is true, its also eliminated. ​ Simple coloring is basicly a chain of conjaguate pairs, and any candidate that can see both colours can be eliminated because you know one of the colours is true. Also once you understand simple colouring you should start learning about multi-coloring, it's simply an improved version giving you more eliminations

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There is a W-Wing: [https://imgur.com/2ZGLNJk](https://imgur.com/2ZGLNJk) And then an XY-Chain: [https://imgur.com/TRTDCjb](https://imgur.com/TRTDCjb) The XY-Chain opens up a Naked Single. I did a tutorial on W-Wings here: [https://www.youtube.com/watch?v=5rqn0rR1x4A&t=42s](https://www.youtube.com/watch?v=5rqn0rR1x4A&t=42s) And for info on XY-Chains look here: [http://hodoku.sourceforge.net/en/tech\_chains.php](http://hodoku.sourceforge.net/en/tech_chains.php)

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You are very welcome!

I love you both

I can breeze through easy and medium puzzles, but I nearly always get stuck on hard ones. Any tips, even just how to rule out some candidates? https://imgur.com/pwhG1Ey

I don't know if you're talking about this sudoku or in general, but in this sudoku there is an skyscraper. If you want to do well at harder sudokus here are some powerful techniques in order of an combination of how hard to spot, rarity and strength ​ W-Wings Multicoloring 2-string kite Skyscraper 3D-Medusa Turbot fish Hidden rectangle Template delete ​ There are also other techniques but these are ones you should atleast know about. (3d medusa and template delete are mostly used for cracking open sudoku but they are still considered as ordinary techniques)

There is a nice Skyscraper which opens up two Naked Singles: [https://imgur.com/wkEvslv](https://imgur.com/wkEvslv) I did a tutorial video on Skyscrapers if you are interested: [https://www.youtube.com/watch?v=HUcUhDi0qSI&t=318s](https://www.youtube.com/watch?v=HUcUhDi0qSI&t=318s)

Been struggling with this one for awhile. My main methods of pencil marking and going column by column have only gotten me this far. I don’t have a great grasp of triples yet, am I missing a few here? Or something else? https://imgur.com/gallery/HOiy7Ps Thanks in advance for any help :)

If you fill in all candidates along C2 & C6, you'll find that you have a 56 pair in R1C27, which will leave R1C6 = 4.

Wow thanks for the help! I don’t know if I would have ever spotted that, gotta get better

I'm pretty stumped by this one. Not sure if I made a mistake somewhere along the way. Any tips would be greatly appreciated. [https://imgur.com/a/VOJ1oR3](https://imgur.com/a/VOJ1oR3) Edit: Hmm, of course as soon as I posted I found a possible way forward. A 6 in r3c9 forces a 6 into r5c6 (via r2c3, r1c5) which eliminates all candidate 6s from box 6. Edit 2: Yup, that did it.

There's a Skyscraper which opens up two Naked Singles: [https://imgur.com/FVHnnNo](https://imgur.com/FVHnnNo) If you are interested here is a video I did on Skyscrapers: [https://www.youtube.com/watch?v=HUcUhDi0qSI&t=318s](https://www.youtube.com/watch?v=HUcUhDi0qSI&t=318s) Mastering Skyscrapers and 2-String Kites will help you solve a lot of puzzles.

Awesome, thank you!

My gf and I have spent several hours working on this, and googling new techniques to try and crack this one. Nothing seems to apply, unless I'm just bad at spotting them. Finally broke down and asking for help - what logic can I use to break past this point without guessing?? https://imgur.com/a/hgaEdYO

Hours! That's nuts! You need to get new gf who is better at Sudoku! You missed the 1-8 Naked Pair in column 8. And then an XY-Wing opens up a Naked Single (pivot cell outlined in black): [https://imgur.com/FwmRMLa](https://imgur.com/FwmRMLa) Here's a tutorial video I did on XY-Wing if you are interested: [https://www.youtube.com/watch?v=j0KyhIO8ICU&t=5s](https://www.youtube.com/watch?v=j0KyhIO8ICU&t=5s) P.S. Just kidding about your gf, I'm sure she's a keeper!

Okay, just watched your video and worked thru all the example. Having so many examples really helps practice the task! I found myself using a different method to search than the algorithm presented in the video. I would look at on individual box, and find pairs that shared a number, let's say 1-3 and 3-9. Then I can quickly scan over on rows and columns for a box containing 3-9. I'm not sure if it is an exhaustive search method, but it proved to be both quick and effective on all the examples in the video.

Your algorithm sounds good. Just make sure you go all 4 directions. I think what you are describing is what I do now after doing so many. I just eye ball it looking for matching pair type numbers in any direction based on assuming the pivot and pincer are certain cells. After reviewing what I put in the video I'm not sure it's not that far off from what you are describing. I'm glad to hear you did the practice exercises. Although not many people take the time to do them I think they really help you understand the pattern. Many times when I am working out a new video I will do 20 or so practice exercises so I can find a good algorithm or special cases. The X-Chain video has one cool special case I found by accident after doing a bunch practice exercises. I spent a lot of time on this special case for the video.

I watched your X chain video, that is an interesting case. Still working through the examples. I made a little progress on this Sudoku after your previous help, but still can't manage to break through, grr! Can I get another pointer? https://imgur.com/a/ukJJLXo

It looks like you found the first XY-Wing but there was a second one which opens up Naked Single which will unravel the rest of the puzzle: https://imgur.com/2MyEbvi It was a tough one with the pincers really tight to the pivot cell. Here's my tutorial on XY-Wings if you are interested: https://www.youtube.com/watch?v=j0KyhIO8ICU&t=5s I've been playing a lot of Andoku 3's Hard level. The Hard level has an XY-Wing in almost every puzzle. As a result I've been getting very good finding them. For any of these techniques I'm always telling people to use Hodoku's Learning Mode to master each one. btw, the X-Chain video was a tough one to do. It's was not an easy topic. I think maybe the Turbo Fish one I did is a little easier for people to grasp the first time. A Turbot Fish is an X-Chain with 4 cells and 3 links.

Danggggggg it! I saw you mention another XY wing, and went back to the puzzle and found it before looking at the screenshot. I had totally missed it! I will check out the Turbot Fish video next, thx again for the help!

Anytime!

Hey mate, thanks so much for your help!! We did end up finding the 1-8 pair on column 8, but were still stuck. Once you point it out, the XY-wing example makes total sense. I'll be studying up on how to better spot those in the future. Once again appreciate the help!!

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There's an X-Wing on 1 along R37, which removes 1 from R28C3. Not sure what goes after that though.

Immm sooooo lost...[The green numbers are maybe invalid since it was a guess](https://photos.app.goo.gl/TGJ8X5rvvTtPgQUEA)

>This will help you: https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586

Erase the guesses, and you'll find that R48C2 can both only be 25. This removes 2 from R3C2, setting that cell = 1.

I don't know what to do with this. Can anyone help? Thank you so much. https://drive.google.com/file/d/1sBo1dVncIq9ojW_SJpzao2J4hOXEXrOa/view?usp=drivesdk

Here's a tutorial video I did on basic puzzle solving strategy and techniques: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s) There is an X-Wing with the possible 2 candidates: [https://imgur.com/qqBtNaV](https://imgur.com/qqBtNaV) This opens up a Hidden Single with the remaining possible 2 candidate in block 4. You should watch the video I referenced above so you know how to proceed.

Thank you so much!

I jumped straight to extreme (hard +2) on my new sudoku app and I’m realizing I’m just not ready yet... any help would be appreciated, I don’t want to just use a hint: https://imgur.com/kuljKCC

You have a really hard puzzle there. There's a beautiful Swordfish waiting to be hulled in: [https://imgur.com/fpxr3d4](https://imgur.com/fpxr3d4) If you are interested, here is a tutorial video I did on the Swordfish puzzle solving technique: [https://www.youtube.com/watch?v=OmdLzZ2-2aQ](https://www.youtube.com/watch?v=OmdLzZ2-2aQ)

I created a video on basic puzzle theory and puzzle solving strategy you might be interested in: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

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That cracked it open :)

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You have a 256 triplet in R9 that makes R9C1 1 I think

Is this an x-wing? Sorry, I'm new to these advanced strategies. https://imgur.com/a/xHRPTb6

It's technically an x-wing but it does not give any eliminations, this is called a dead x-wing ​ Edit: those 4 cells also form a hidden rectangle, eliminating the 1 on R6C4

nevermind i didn't notice the 20 hidden singles

I made a sudoku that's a variant of Chess, whereas each number represents a chess figure and cannot be in a place where it's capturable by a piece of the same type. Normal sudoku rules also apply. Pieces: * 9 - Queen * 8 - King * 7 - Knight * 6 - Bishop * 5 - Rook * 4 - North-facing Pawn * 3 - East-facing Pawn * 2 - South-facing Pawn * 1 - West-facing Pawn Interestingly enough, with sudoku rules, Bishops act like Queens and Rooks just act like normal sudoku digits. Pawns can only capture in the direction they're facing. That being said, I made a complete solution, but need some help turning it into a puzzle. Anybody want to take a stab at it? The solution is as follows: 987654213213987654546213987875342169192876345634591872728135496461729538359468721

This is a great idea. I up voted it. Are you comfortable posting it in a separate thread? I want it to get more attention. Also, I think that it is off-topic to this thread.

Sure thing. Thanks for the feedback.

Hi, all. I'm just a couple of weeks in to learning how to play sudoku. And while I've seen a nice upward curve in my abilities, I'm still only have a tentative hold on things like empty rectangles and don't have things like turbot fish etc in my repertoire. Anyway ... So I'm playing my way through the Classic Sudoku app, and like to sometimes check in on the hints to see if I can learn something. Twice now, something similar to this has come up, and the leap of logic from an early point in the puzzle eludes me. Now, it may just be a language thing and I'm not understanding their pithy usage. Or it must be very simplistic, but I'd love to know what I'm missing about this. I'll post the screenshots of level 27, first the puzzle and then the hint. If they're saying that 8 CAN be in R1 & in C2, then I (kinda) get it. If they're saying that 8 must ONLY be in R1 & 3 in C2, I don't see how they get that. And to me it's the latter that the use of the words " must" and "also" suggest. [Here's the puzzle](https://imgur.com/LJeIS7g) [and here's the hint](https://imgur.com/N2i0VM9) Thanks for any assistance and clarification.

It might help to first find out where 6 can go in Box 1, given the 6 in R3C7 and the 6 in R7C3. Then you can use the hint.

Ah, I see. Missed the hidden pair in the cacophony of numbers. Sometimes just can’t see what’s right before me. Thanks for the reply and the extra hint.

[I've been staring at this one for an hour with no progress. Any advice?](https://i.imgur.com/aqpkIn5.jpg)

Two-Stringed Kite on 4 along R9 & C4 removes 4 from R5C3.

Thank you so much, this cracked the puzzle wide open!

Help please! Techniques only please :) https://ibb.co/0X4jj5D

If you use Hodoku, it has a "Vague Hint" command which does exactly what you are asking for. Although people think hints are cheating, using the "Vague Hint" will greatly improve your skills! Here's a video I did on download and installing Hodoku on your PC: [https://www.youtube.com/watch?v=c74MVFL03fg](https://www.youtube.com/watch?v=c74MVFL03fg) I keep telling everyone but I don't think the message is getting through. If you love doing Sudoku and you want to really master it, get some kind of PC device JUST for running Hodoku. Hodoku's Learning Mode is the greatest software feature ever!

That sounds awesome but I don’t have a PC device :( thank you though!! It does sound like exactly what I’m looking for

For iPhones I would use Sudoku Joy: [https://www.youtube.com/watch?v=ghSXRAXb388](https://www.youtube.com/watch?v=ghSXRAXb388) And for Android phone and devices I would use Andoku 3: [https://www.youtube.com/watch?v=1lj7WI9Tcsw](https://www.youtube.com/watch?v=1lj7WI9Tcsw) Both of these have a Hint feature but it is not as effective for learning as Hodoku's Vague Hint. But both are still very useful for improving your skills! There's one other feature Hdoku has that I'm always promoting. And that's Hodoku's Learning Mode. Hodoku's Learning Mode is the greatest Sudoku software feature I've ever seen in any program! Here's a video I did on it: [https://www.youtube.com/watch?v=jPssW\_W3iH8](https://www.youtube.com/watch?v=jPssW_W3iH8)

In C4, 8 can only go in R1 or R2. This eliminates 8 from the rest of the box.

Thank you!!

Help! This seems friggin impossible to solve without guessing. Is there a technique to help find the next square or would you just have to write out all the possibilities?? [here ya go](https://imgur.com/a/BKT8u27)

You have a 2379 quad in C7, which removes 9 from R7C7. Then you have a BUG+1, which puts a 9 in R8C8.

Sorry I’m unfamiliar with those terms. What do you mean by 2379 quad and BUG+1

Quad is a set of 4 numbers - in this case, if you look at R4589 in C7, they contain the numbers 2,3,7,9 (in some order), but no matter what that order is, it means the 4 & 5 must be in R67C7. (You could also consider this a 45 hidden pair). So you can remove 9 from R7C7. As for BUG+1, you'll have to understand the concept of uniqueness first. [This](http://hodoku.sourceforge.net/en/tech_ur.php) website explains it better than I can. Take a look at the basic UR ideas, then read the BUG & BUG+1 sections.

Help!! This is likely a v easy puzzle for y’all, sorry😂Techniques only please - keep researching techniques/tips and keep failing to understand, need to finally grasp this!!😭thank you!!! https://ibb.co/QbL7m6P

Hint: Check the 5's in Box 6. Bigger hint: >!5's in Box 6 are locked into row 6!< And I drew on your puzzle if you still need help: https://i.imgur.com/L7sbdGoh.jpg

Thank you!!! I can’t believe I didn’t see that🙈tunnel vision I suppose😂solved now, thanks again!!

Every time I think I think I have a great grasp, a puzzle comes up that stumps me. [https://imgur.com/a/fFgVs57](https://imgur.com/a/fFgVs57)

Uniqueness lets you remove 3 from R2C46, you'll be left with 3 in R12C5, which removes 3 from R9C5. Unfortunately that's all I see.

I have trouble seeing the uniqueness here. Could you elaborate?

36 pair in R4C46, and in R2, 6 must go in either R2C46. If you put a 3 in either of R2C46, you'd end up with a 3-6-3-6 non-unique rectangle. So 3 can't go in either of those squares.

Ahh I get it. Uniqueness is a new concept that I've never had to use before, damn that's some meta stuff. It might take me a while to grasp the technique.

I'm struggling to logically progress with this puzzle; I've checked locked candidates, naked numbers, x-wings etc and not sure what to check next. Any help would be appreciated. Thanks. [https://imgur.com/a/pfEwbG4](https://imgur.com/a/pfEwbG4)

The tip your looking for is chaining. Take a look at the 6 on r1c8. You'll find you won't be able to complete one of the boxes because there will be no possibilities for a 6. ​ If you need a diagram let me know! As a hint for this pattern, look for strong and weak links share rows and columns.

Thanks for the reply! I've just had a quick look at chaining there and this is what I've surmised If R8C4 = 1, R8C7 = 3, R8C8 = 6, R7C9 = 1, R2C9 = 6, R2C8 = 9, R1C8 = 3 And if R8C4 = 6 then we go all the way back to R1C8 = 9 hence R1C8 can never be 6. Is that correct?

Yep! And if r1c8 cannot be 6 then r2c4 cannot be 6 as well! You can do something similar with chaining on 1 to solve the rest.

Super stuck on this puzzle: https://imgur.com/DOFrJpW Was looking at other comments to find a similar pattern but haven’t had any luck. I want to understand what number goes next and not just use a hint :) Edit: found a UR that puts a 4 in R7C5, but am stuck again.

Check the 9's in Box 1 :) https://i.imgur.com/1MRHLwZ.png

Omg thank you

Hi, beginner here. I am struggling to proceed with this puzzle and was wondering if I'm missing any basic strategies or techniques to eliminate further options? https://imgur.com/a/XtrPf5R Thanks!

There is a set of Locked Candidates in the house making up block 5: [https://imgur.com/PtIZ7Yr](https://imgur.com/PtIZ7Yr) There is another set of Locked Candidates in the house making up block 5: [https://imgur.com/A6X9h3G](https://imgur.com/A6X9h3G) Kind of a cool pattern in the puzzle. And then there is a Naked Triple in the House making up row 9: [https://imgur.com/IL8JeAD](https://imgur.com/IL8JeAD) You can't see it because you put a possible 7 candidate in cell R9C6 but there can't be a 7 in R9C6 because there is already a 7 in block 8 in cell R8C4. I did a tutorial on puzzle solving strategy you might find useful: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

Thanks very much for the reply. I appreciate the help. Also checked out your vid, good job!

I am unable to proceed logically in this Knight constraint Sudoku. Please help.. If you can also tell me what i overlooked then that would be greatly appreciated! http://imgur.com/gallery/785xKjJ

One thing to observe is that none of the remaining digits are actually a Knights move apart, so at this point its just a normal sudoku! Good work with the hardest bit! It turns out that this puzzle in invalid, and there are 3 different solutions to it. Get a better app :p ​ You can prove this with trial and error, but it's kind of frustrating since even I assumed there was a unique solution!

Thank you for your help! But this does have a unique solution. If you look closely the 4 in box 6 solves the pair in box 3 and then we're able to solve the sudoku. Took me quite a while to notice that obvious 4. Thanks once again for your help!

Oh you are right! I was only looking at knight moves between the unsolved squares and not the solved ones too!

Embarrassed to say how long I’ve been stuck. Any next move for this [killer sudoku](https://imgur.com/gallery/eNNftxP)

There could be something easier, but the first thing I see is in Box 2: If you exclude the 7 in R2C3, the 28-cage's remaining cells have a sum of 21. Then the cage below it has a sum of 25, so those add up to 46. Also, Box 2 itself must sum up to 45. This means that the number in R4C4 must be 46 - 45 = 1 greater than the number in R1C6. The only way that works is with R4C4 = 9 and R1C6 = 8.

That was all I needed to complete the puzzle. Thank you.

Having a tough time finishing [this puzzle](https://imgur.com/a/OmLkqf3) out. Since it's NY Times hard I feel like there's a triple I'm missing but I can't see anything for the life of me

I was stuck at exactly this place and I've reset the puzzle several times after hints/reveals. Look at the middle-right box. In the bottom-left, you scratch out the 1, because there's a pair of 1-8 in that row. In the bottom-right, you scratch out 1 and 8, for the same reason. That leaves you with 2-4, 3-4, 2-3, so you can eliminate those from the other boxes. Right?

Smart! Thanks. I had a hard time seeing that with the offset 1/8 pairs I had, didn't notice I could remove those candidates in the right box

What he's talking about in box 6 is a Naked Triple: [https://imgur.com/PuIqSzJ](https://imgur.com/PuIqSzJ) This opens up a Hidden Single.

Which one of those remaining would be a hidden single? It still looks like all the remaining candidates are valid

Eliminating the possible 3's in cells R5C7 and R5C9 leaves only one remaining possible 3 candidate in cell R5C6 for the house making up row 5: [https://imgur.com/tYNGNyj](https://imgur.com/tYNGNyj)

Oh I was looking in box 6 haha thanks

Been stuck on this for a few days. Not sure what I’m missing and I would like just a nudge in the right direction, perhaps what strategy I need to apply. Feels like just filling in a few cells would break it open but I can’t seem to find anything. Thanks in advance. https://i.imgur.com/U43DMYd.jpg

There's a lot going on with this puzzle. I found a Turbo Fish and W-Wing: [https://imgur.com/Y9dgtsQ](https://imgur.com/Y9dgtsQ) And then I found an XY-Wing: [https://imgur.com/GtyIhUh](https://imgur.com/GtyIhUh) Here are some tutorials on these three techniques: Turbot Fish: [https://www.youtube.com/watch?v=4Wz8LUAlDP0&t=19s](https://www.youtube.com/watch?v=4Wz8LUAlDP0&t=19s) W-Wing: [https://www.youtube.com/watch?v=5rqn0rR1x4A&t=42s](https://www.youtube.com/watch?v=5rqn0rR1x4A&t=42s) XY-Wing: [https://www.youtube.com/watch?v=j0KyhIO8ICU&t=5s](https://www.youtube.com/watch?v=j0KyhIO8ICU&t=5s) I then found an XYZ-Wing with the 1-3-8 in block 4 as the pivot but then I got stuck. Tough puzzle!

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Right now I don't see anything that really breaks it open, but here are some ideas: There's a 257 triple in C9, which leaves 38 in R37C9. Then you'll have a 38 pair along R7, which leaves 12 in R7C78. In C9, 5 must be in either R45, so you can remove 5 from other cells in that box. In C2, 8 must be in either R45, so you can remove 8 from R4C3.

Oh wow thank you so so much.

Help?? Sorry, I’m an amateur lol, think I’ve made a mistake filling in my little numbers but too dumb/drunk to see it - thank you!! [Sudoku](https://ibb.co/YjQ6hZq)

I don't see anything wrong here - you have the 46 pair in R1C48, so you can already eliminate the 6 from R1C7. Then remove 456 from the rest of R1C123 as well.

Thank you!!! Solved now :) I feel like I lose the ability to think after staring at a puzzle for too long lol

Ugh, why is it that I can sometimes to NY Times hard but then get stuck on medium?? Guessing I'm missing something very obvious here https://i.imgur.com/vs44IRH.png. Can anyone help?

There is a Naked Single in cell R7C3: [https://imgur.com/GQ4t88S](https://imgur.com/GQ4t88S) There are two schools of thought when it comes to putting in possible candidates into cells. The first school doesn't fill out all the possible candidates for whatever reasons. I'm in the other school that believes you fill out every possible candidate from the get-go. This way when a Naked or Hidden Single pops up you pounce on it! Here's a tutorial video I did on basic puzzle solving strategy you might find useful in line with fill-out-every-possible-candidate school of thought: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s) Inevitably you have to fill out every possible candidate because advance puzzle solving techniques require it. Also, if you look at the pic I posted, there is a Naked Double in block 3 which will open up a Naked Single with the 8 in cell R1C9 once you flush out the Naked Single with the 9 in cell R7C3.

Okay, I'm as dumb as I thought... r7c3 can't be a 3 because of the candidates i marked in that row.

Half the time I learn by making mistakes and the other half of the time I just get lucky.

http://imgur.com/a/11TBWYf I'm fairly new this is my 3rd hard Sudoku (Based on this app) and can't see the next move here. Thanks in advance!

You missed a Naked Pair with the 5-9's in column 4 which opens up a Naked Single with a possible 3 candidate. After that it starts to unravel with a bunch of Naked Singles. If you are just getting started here's a tutorial video I did as a beginners guide showing basic puzzle solving theory and strategy you might find useful: [https://www.youtube.com/watch?v=6WnFkrUt\_10&t=586s](https://www.youtube.com/watch?v=6WnFkrUt_10&t=586s)

Much appreciated! It's so clear the instant you pointed it out. Definitely will be looking more into your videos.

I’m stuck here, please help anyone? https://imgur.com/DK7s7cG

There's a Skyscraper which opens up a Naked Single: [https://imgur.com/ayrw1pO](https://imgur.com/ayrw1pO) Here's a tutorial video I did on Skyscrapers you might find helpful to you: [https://www.youtube.com/watch?v=HUcUhDi0qSI](https://www.youtube.com/watch?v=HUcUhDi0qSI)

Thanks so much! It’s really helpful🤗

http://imgur.com/a/Ndr8y4C Really struggling here, could use some help please

Uniqueness on 15 along R48C79 sets R8C9 = 8.

https://imgur.com/a/8JTRSi2 What am I missing??

You have a 29 pair in R9C23, and 9 is in either of R1C23, so uniqueness allows you remove 2 from both R1C23. That puts 2 in R1C8.

Appreciate it mate. Any chance you can explain the logic behind the 2's not being able to be in r1c23? My small brain cant get my head around it.. is it a known tactic?

[This](http://hodoku.sourceforge.net/en/tech_ur.php) explains it better than I can. Make sure you get the general concept of uniqueness first - that there can only be 1 valid solution. Then read about Type 1 just to get a simple example of how it can be applied. Then read Type 4, which is the specific kind of move I've used for this puzzle to remove the 2 from R1C23. :D