Sudoku Primer 79 - solving the 'hardest Sudoku we've seen in a newspaper' (sudoku extreme)
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- čas přidán 2. 05. 2018
- Discover new ways to find numbers in sudoku puzzles. Learn techniques used to solve hard to expert puzzles in this video.
This was requested by subscriber Anish Vij. Solving what the "Cracking the Cryptic" CZcams channel calls the "hardest Sudoku we've seen in a newspaper."
If you like these videos click like and subscribe to this channel.
Go to www.sudokuprimer.com for lots of sudoku techniques and patterns. There are also cool sudoku t-shirt designs in the online store. - Hry
By the way, Cracking the Cryptic used an x-wing and a modified triple to solve the puzzle. However you don't like using pencil marks so you used trial and error as your method of last resort.
Thank you for taking the time to solve the puzzle in your way.
You're welcome. Thanks for the request.
What is a “modified triple”?
@@laurencegoldman4639 An XYZ wing
czcams.com/video/Y4sorf-uj8c/video.html
Thanks for solving this puzzle your way. I'm impressed with your pencil - less recall.. Being an octogenarian my memory needs a short pencil off sheet.
The benefit of my method is the pleasure of the visual record of the logic paths covered. Thanks again for sharing the intimacy of your reasoning. I'm certain I learned from you.
Thank you for your nice comment. I'm impressed that you're solving puzzles in your 80s! That's very good. I hope my videos have helped you.
czcams.com/video/Y4sorf-uj8c/video.html
No need to guess or use pencil marks:
At minute 28:16 you can get unstuck without putting pencil marks because you can see an x-wing of 2's in columns five and eight. That means there are no more 2's in row nine; and that forces the 2 of column three... when you get stuck again, notice that 7 cannot be put in cell at row3 column2 because that forces a 7 in the same column. So the cell in column2 row3 must be a 6. That makes it easy to complete the puzzle.
Very good observations. Thanks for sharing! You're exactly right.
czcams.com/video/Y4sorf-uj8c/video.html
At the point you went to "trial and error", I played without notations with alternating the 27 pair of c8 and the 12 of box 2 and established my impression that the 2 in box 7 was restricted to r7c3, accordingly the 9 in r7c1. Alternating again with the 27 pair of c8, I then proved there was a 267 triple in the centre and left columns of box 3, placing the 9 in r2c9. This solved the puzzle.
Good job solving it!
czcams.com/video/Y4sorf-uj8c/video.html
hard puzzle, good job solving it
Thank you Tim.
In fact the modified triple used by Cracking the Cryptic is XYZ-wing.
Thanks.
I got to 28' 30" on my own and then checked to see if there was a method to get past guessing the 1, 2. I filled in the 1, 2 and it was straight forward again.
I came across a "HARD" one in a paper and still haven't completed it as it has several triplets and a couple of pairs. I have tried a few guesses but still not cracked it. Doing online sudoku, I have completed guesses down to 3 levels but it is easier to backtrack on the PC.
Thanks for this puzzle, Harold.
You're welcome. Good work!
when you have a choice to guess or try something different ... instead of looking to place a number look to exclude a number .... that is possible ... work from the one with the most options down to the least and you generally find one that cant go anywhere but one spot because nothing else would work after 3 more numbers ...
Thanks, that is a good suggestion.
czcams.com/video/Y4sorf-uj8c/video.html
An excellent solution for those of us neophytes who have yet to spot an x-wing etc. It is notable that Mark Goodliffe of CTC fame found that such 'bifurcation' proved more time efficient than Simon's more elegant solution, recently. Simon as someone who delights in the aesthetics of the logic, preferred his own solution, so I guess it is a case of different strokes for different folks.
Well said.
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A tuff puzzle even using pencil marks - to solve it without is well beyond my old brain!
Using pencil marks I found an X-wing and then had to use an Empty Rectangle to solve it.
That's good though. You used two advanced techniques to solve it. :-)
Are there a certain minimum number of cells that must be filled in by the puzzle maker for publication? Or can it be any?
Thank you for your question. I'm sorry i took so long to reply, I was out of the country for three weeks.
Research has been done on this. The number of "givens" (givens are clues, or numbers that are already filled in for you) cannot be less than 17. It is believed that a puzzle with 16 or fewer givens cannot be solved.
i wish i had a memory like yours.
Thank you. Keep doing puzzles and your memory will improve!
I put this puzzle into HoDoKu and solved it using only simple techniqes: eliminations from naked pairs, naked triples and locked candidates (type 1) and one elimination from an x-wing. then just hidden and naked singles. Took about 15 minutes.
Very good.
czcams.com/video/Y4sorf-uj8c/video.html
Hi, I am Andrew L, the 80 year old man. I have asked for help in your Sudoku Primer # 183 and #204 for the issue of quadruplets. I am still confused with your answers yet.
Here, in this # 79, I have some suggestions to break open your choice of [1 and 2 in Block 2] that compels you to choosing the [last resort of solving by guessing].
At 19:08 of your video, after you placed a [6 in Block 9], the [column 7 of blocks 3, 6 and 9] is extremely helpful to solve the whole puzzle.
[a] there is an [empty wall in column 7 in block 6] with 1236 already placed in remaining places of block 6;
[b] that means the 1236 should be placed in column 7 of block 3 and block 9;
[c] that means you find the identical twins of 12 and 12 in column 7 of block 9;
[d] then you have a [7 at r9c8] and a [2 at r3c8];
[e] then in block 2, you would know that [1 is at r3c5] , and [2 is at r2c6].
Then everything that follows should be easy.
Thanks for the patterns teaching in your sudoku Primer website. I learned a lot and have benefited from it, including finding the above suggestions.
Using [x-wing of 2 in columns 5 and column 8] can also solve the issue; but I am bad at finding x-wings.
Thanks again for your patterns and techniques teaching.
Thanks for your comment. I'm sorry I've been slow responding; I have been extremely busy lately.
When you find the 12 twins in block 9, r7c7 could also be a 7. Yes there is a 1236 in block 6 but there already is a 3 in c7. That means the remaining empty cells in c7 (outside of box 6) could be 127 in block 9, and 679 in block 3.
I like your thinking, though. That is a good "alternative" way of looking for ways to eliminate numbers. And I'm glad my website has helped you!
@@wordoku I admire your unique talent in remembering so many twins and triplets simutaneously while proceeding to locate other digits in the puzzle. Too difficult for the old man; and if I remember wrongly I would make a wrong deduction that follows. I would prefer making visible snyder notations.
Secondly, back to this puzzle, when you have 3 and 6 already filled in block 9, the [1,2 twins in r7c7 and r8c7] would automatically make the [r9c8 a 7]. Then we have [r3c8 a 2]. Etc.
Anyways, thanks for your patterns and the double row\column elimination technique.
i buy the sudoku books that have easy to very hard sections. what i dont quite understand is how they sometimes determine what is hard and what is easy. i skip the easy ones and breeze through most of the very hard ones. when i go back to fill in the remaining puzzles i find i have trouble with some no matter what the level is. what's up with that. i hope you answer this.
I'm sorry I am slow responding. I was out of town for two weeks with limited internet access.
Thank you for your comment. I'll try to answer that based on my experience.
Each publisher has their own way of determining the complexity of each puzzle. Some publishers use "expert" while others use "diabolical" or other names for their hardest puzzles. Because of that there is a large difference between publishers and how they both rate and name skill levels on puzzles. There is no standard.
I have also noticed that puzzles marked hard, for instance, are sometimes harder than the puzzles marked expert, even with the same publisher.
One thought regarding going back to fill in remaining puzzles: I have solved the same puzzle twice and solved it a different way each time. When I've done that I notice that first way is sometimes harder or easier than the second way I solved it. So when you went back you may have missed some numbers that you may have found earlier.
I hope this response helps you. Good luck!
@@wordoku cheers harold, that was helpful.
Keep in mind that when you decide to use trial and error, sometimes some puzzles will reveal more than one solution. I've come across this several times.
If a puzzle has more than one solution it isn't really a valid puzzle.
I agree! So how does one know after solving if there were another solution?
Almost all sudoku puzzles are valid. I think you can safely assume all puzzles are valid.
It works out if you put the 1and 2 in the top middle box the other way around. I was stuck near the end (I chose the 7 and 9 in the top right box because it looked easier) either way around works.
I used two different coloured pens to show the results of the two different placements of the 7 and 9. As I don't have your ability to keep two different number patterns in my head at the same time without getting them confused.
There's only one solution to a sudoku puzzle
At 19:06 you placed a 6 on the bottom right square (8,9), in between the 4 and the 8. Another possible 6 in the same square was (8,7). But you could have placed a 6 on the same column between the 1 and 3 (2,9) as well as (2,7) (top square). You just got lucky that the 6 was guessed in the correct place.
The numbers left to fill in row 8 at that time were 1246. And there is already a 124 in column 9. So the 6 has to be in r8c9. You can also see that the cell at r8c9 can see all of the other 8 numbers - 1234 in column 9 and 5789 in row 8. So the 6 can only go there.
czcams.com/video/Y4sorf-uj8c/video.html
I got stuck at same stage as you but arrived there much quicker than you and noticed no comments on this strategy...Work on horizontal block of 27 numbers. Start at top block then middle block then bottom block. Then work on vertical blocks of 27. Left block then middle block then right block..[or vice versa} As you have added numbers during this process repeat all 3 horizontal and 3 vertical blocks and after 5 minutes you will be at same position it took you 25 minutes.. Nevertheless,good suggestions in comments to improve my solving options.
Thanks for your suggestion! I have learned techniques from others in the past when they have left comments. I appreciate it.
@13:44 "I don't think that helps us much." But the 5 you just filled in on (1,7) implies 5 in (7,8).
Yup. Good catch!
Really great puzzle! Thank you Harold! But it's so hard to follow without pencil Mark's, when we don't have your brain!
At 15:40, after placing the 5 in r6, there is a naked 6 in c9r8
This gives a 14 double in c2r8.
By choosing a1, the puzzle then solves completely and easily with no further strategy.
The power of a what if?
Really interesting puzzling. Thanks so much. Chris.
Again, great to see other ways of solving. Thanks for your comments.
czcams.com/video/Y4sorf-uj8c/video.html
@10:40 you start looking for 6s... I know it's outside your approach, but in cell (8,9) you can eliminate everything except for 6 so (8,9) must be a 6.
Yes, you used solving for a single cell, a technique that I could have used. (8,9) is obviously a 6.
In the 6th col, you get a triplet and if we use this the problem gets solved without a guess....sundar
@@ramaswamisundar I looked at your comment and I don't know at what time you see the triplet. Please enter the time you're looking at and more detail about the triplet. Thanks.
i have no problem in solving even extreme level in Sudoku primer(i dont use pencil to mark possible entry).
But in app sodoku by Brainium, i cant even start. The max number in small box is no more than 3...???
Yes, I use the Brainium sudoku app on my mobile phone. The hard level is about the same or somewhat harder than diabolical in Sudoku To Go puzzles. The expert level is harder.
Is there a way to change the settings?
My version app of Sudoku allows different settings, 3 strike rule, pencil marks etc. Look around for a different app.
Please hold the pen on the back end if possible while scanning the puzzle so we can see. Thanks!
Thanks for the reminder.
Hi, sorry for english, if you put 1 in column 2 of block 1, you can find out that 1 can be only in column 5 of block 2
Your English is good! Can you tell me at what time in the video you saw that?
@@wordoku I stopped the video, and did sudoku by myself, after solving returned the video, it took me hours to solve, I got stuck after putting 6 in block 9
That's what I say too, *_ghost numbers_* .. ☺
Very good!
hi harold the most difficult puzzle i have solved had 10 trial and errors in a row
Wow that's some serious solving! That would take a long time to solve too. Do you remember how long it took to finish it?
well my program did it in 4 minutes using a table of 1024 combinations of 1's and 2's 10 long eg 1111122222 it kept going until it hit the right combination. i cant solve puzzles as good as you thats why i wrote the program
Hello sir your solutions (solving using twins or triplets!) are amazing. I loved it but i also solved this puzzle.. This puzzle don't need a guess like 50%-50% chance you can simply solve it using writing small numbers (candidates/possibilities) try to use pencil on hard puzzles. Thank you hope you reply me something special
Thank you for your comment. I like hearing from people who watch these videos. I appreciate what you said about marking candidates. I have done that in the past and it works good. I like to solve puzzles without using candidates. You see the puzzle differently. I think you would also like Sudoku Swami - another sudoku channel on CZcams. He does use candidates.
czcams.com/channels/dh4SoUiHPACqY1SGumgKYQ.html
This is the most PAINFUL Sudoku solve I've ever had the misfortune to watch :( Extremely sad for the need to result to Bifurcation when logic would suffice.
I think my newer videos are better.
czcams.com/video/Y4sorf-uj8c/video.html
Are you the person that wants to enjoy the suduko journey ,or were you cursed like me ,and on your first puzzle wonder if you could design the hardest one, there are two paths
The first one.
Damn Harold, have you ever tried playing chess? You may have grand_master potential ! yes, this is a really hard puzzle ( with your technique ). BUT, I finished it in record breaking time. About 30 minutes. I have watched lots of vids by " the sudoku guy. There is no way I could do a puzzle without the helpful notations.
Thanks for your comment. You're too kind! If you solve without notations for a time you will find that it gets easier. I think it's a good brain exercise.
czcams.com/video/Y4sorf-uj8c/video.html
You missed the first 5 for a long time. The pencil drives nervous. You should mark "ghost numbers" so you don't need to find them several times. You should concentrate on well filled lines, rows or sectors with the most numbers already found before you prove the ones with fewer numbers.
A new found number could often furthermore implicate several solutions with that number in other sectors - so you should follow them first.
The techniques you use could be explained in a half of the time this video needs.
Thanks for your advice.
I can see your hand moving all over without any commentary. Please write in the hidden twins.
This channel is dedicated to solving sudoku without writing candidates. I hope you find it helpful even though I don't mark them.
Nice videos and voice. Ignore the foolish comments, they're a little angry because you don't use any cheats.
Thank you. I prefer solving without marking candidates.
@3:33 When you first scanned for 5s, cell (2,2) must be a 5 -- where else in column 2 could a 5 go? :)
Yes, you're right. Sometimes I'm trying to point out a technique so I'm focused on that and other times I just miss them. This time I just missed it!
Took my under five minutes, how was that hard !,then again I used pencil marks
do it in your head ... from the screen took me all of 12 minutes ... yes i do them often
Good.
Very good!
You're doing very well.
I used to say the Xterme puzzles were easy ,cause of the added 'clues,/restrictions' ,buy a friend gave me one that took me 3 hours, it's in my collection,it gives you nothing under suduko rules ,the giant X wing in the Xterme puzzles only gave you were a number could be here or there in a block ,and there were no 3 in a row ,up or down in a block ,so you fill in csnidates ,snd when your done doing all that work ,no chains ,x,xy xyz, work, no loops ,then if you guess, you cultisac were ever you go ,it's a good one ,who ever came up with it is to me ,THE MASTER, but with a lot of pencil, lot of erasers, and paper worn so thin ,you realize there's another way to fuck this puzzle uo ,I got it! Thems puzzles,and I'm a collector ,there isn't many of them
Very good.
I copied the puzzle at the beginning of the clip and was able to solve it in about half an hour, which is odd because I spend more time on some of the easier puzzles.
Some puzzles just flow. This one flowed for you!
I didn't realize that I had made the same comment a year ago, you're absolutely right some of these just flow.
Solved in 5:18, no special techniques.
What was this puzzle rated?
CtC has had much more difficult puzzles than this, I think.
The "hardest sudoku we've seen in a newspaper" is what the CtC guys "rated" it. I don't know what the original creator rated it. Good job solving it so quickly!
@@wordoku I must have lucked out... sometimes you hit on the right order & it just falls almost by itself.
@@julieannmyers8714 Yes, I know what you mean!
I'm not sure how the "wall" gave you an 8 in c5r7.
Thanks for your question. There are 58 twins in box 8, in r7c5 and r8c4. There is already a 5 in box 2 (in column 6) so the wall pattern in box 5 constrains the 5 to column 5. Therefore the 5 can't fit in r7c5 in box 8. Because of the twins in box 8 mentioned earlier r7c5 must be an 8. Start watching at 6:10 - it is explained there that box 5 has "ghost 5s." See www.sudokuprimer.com to read up on techniques like ghost numbers, and patterns like the wall pattern.
by 4:11 you missed a very obvious simplification .. when you did the 4's to the top right square ... you failed to notice the middle right square had a full middle line which forces a 4 on the far left line of that square and forces the 4 to the middle square of the top right square ... when starting with the number sequence when you see these filled lines ALWAYS check closer the squares on BOTH sides of the filled line because one of them will have a number that can be placed the majority of the time .... and btw it's not a hard puzzle ... took me 12 minutes ... yeah I paused the video and did it ... it does get a little tricky but being able to see all the possibilities does make it easier
Thanks for your suggestions. I do miss some obvious things sometimes. I may just miss them but I may also be focusing on a concept I'm trying to teach.
czcams.com/video/Y4sorf-uj8c/video.html
Because you don't go into any detail you are suspect as just filling out a puzzle you have answers for.
This video was published over five years ago. I used to go through the entire puzzle. Try some of my newer videos, where I skip all of the busywork. And I feel like I've improved a lot over the years.
Pleas send me solving rules of Diabolical sudoku puzzles
Go to sudokuprimer.com/techniques.php to find a list of techniques to solve all skill levels of puzzles.
I think Xwing is needed. Unfortunately I don’t understand it well. A bit disappointed with this one
They used an x wing in the other video. See the link in the notes.
i solved it in 20 mins.... seen harder puzzles then this
I agree, it isn't the hardest.
"It's getting hard, so guess" Cheers, really useful.
BTW there were another 4 or so guesses that could have been made.
Getting stuck, and then making an intelligent use of T&E, okay. But to do the simple stuff and then make a lucky guess gets nobody anywhere.
I'm an average player, and got to where you gave up in about 10 minutes. That's what was interesting, as a puzzle; it just dropped on you out of the blue, one minute easy, and then it came to a stop.
No it doesn't help.
Very good!
Before you watch the tutorial just copy the puzzle, it took me 25 minutes to solve it. I never watched the video.
Very good!
I did
Good
Not teach ing, all in your head does not help me. Glad you could solve it!
I think my newer videos are better. I hope I'm improving.
My program solved this puzzle in 2 seconds
so you really didn't do any work at all. nice going
Very good!
It took me more than two years to write this program in just basic. It wasn't easy. I knew it could be done. The computer is faster than us.
I am a software developer, I've been writing software since the 1970s. I haven't tried to write software to solve sudoku but I can imagine how difficult it would be and how long it would take to write it. I'm impressed! That's quite an accomplishment.
@@wordoku I have worked as a programmer since mid 70's I worked with pick basic. I used just basic because its all I could find. I can send you a copy of the program and an audit trail of what it does to solve the hardest puzzle you can find. It has been a challenge. I don't know anyone thats interested in sudoku.
Can hardly hear you and your hand is in the way too much of the time
Thanks for the critiques. I have had others tell me that too so I think my newer videos are better.
Watching this gave me nothing but a headache
Es tut mir Leid dass es Ihnen nicht gefallen hat.
Nothing really difficult about this one, a normal run of the mill one.
That's v silly my friend! This was pretty tricky!
For the geniuses that find everything easy, what are you doing here? leave us medium intelligent persons that want to learn do it, without making us feel like idiots.
Very good. You know this very well. By the way, the "hardest sudoku" moniker was given by someone else.
Seems a very slow an inefficient way.
Yes, not the fastest. But I wanted to show this as an option, and show how it is done. Thanks for your comment.
This was painful to watch as he repeatedly developed conclusive constraints then failed to act on them or record them (pencil marks), only to rediscover them later.
What a waste of time watching this. The whole point is NOT to do trial and error and work out the logic.
You're right. But trial and error IS one way of doing puzzles; whether you want to use it is up to the individual. So it's good to let people know it is an option.
Not sure I agree. Sudokus are created so that logic can be used to solve them. Working out the logic, even if incredibly difficult, is what gives the satisfaction in solving the puzzle. This was a difficult sudoku but not devilishly so. If you had posted this video as ‘Using trial and error to solve a hard sudoku’ how many views do you think you would have got. The fact is, someone had to invest quite a bit of time before realizing there were going to be no insight, no neat logic tricks or ideas because the author only knows how to eliminate or find numbers by doing simple row and column cross checking multiple times and then defaulting to brute force when all is lost. Which means that almost any puzzle beyond simple ones would appear difficult as they will require some other form of logic to resolve.
lasted about 20 seconds after you started, no pencil marks, you were going to take too long, bye.......
Well, thanks for looking anyway!
I got some mf hard ones,they don't make the circuit ,cause there not fun,my Collection of hard ones I call 'hair pullers '
I love those ... spend more time finding where something cant go than where it can ... then all of a sudden poof a number falls in and next thing you know it's done ;)
You're right!
Such a long winded way to solve
Yeah, this is an older video. I hope I have improved with newer videos.
I dont like very hard puzzles.Takes the fun away.
I agree. I like puzzles that make me stretch to figure them out but don't like those that take forever to solve!
@@wordoku Do you own any other books besides Sudoku to go? I have lots of books by many different people. Some good some to avoid buying
I do. I have Dell and Kappa books. I have used a couple of different apps on my phone, and tried puzzles on different websites. I like Sudoku To Go because the puzzles are larger and the paper is better quality. I've tried other more obscure books too.
@@wordoku I have a lot of big thick books bought on Ebay and thriftbooks.I buy them cheap mostly around 5.00 shipped. My very favorite book is called...Best ever sudoku....Its a big book large print. And puzzles are very fun. Google up this isbn number for it 9781474867320.Found it at Booksamillion for 12.00 but I bought mine from Discoverbooks for around 7.00 shipped. Buy it and you will love it.
Thanks! I'll look into it.
You r just guessing no trick or rule
If I were guessing I would surely get some of the numbers wrong, and wrong numbers would be obvious. I do use techniques that don't require pencil marks. Puzzles are solved differently when you don't use pencil marks.
Sudoku 79 can't understablevwhat has he been droning just murmuring ....
I think my newer videos are better.
Disappointed. I solved it before even watching the video, so I didn't watch the vid. "Hardest Sudoku" - my chapeau.
Good for you. You must be very good at sudoku!
@@wordoku Hi. Me? Average at best. My beef is with the description. It really was not a hard Sudoku. The only tricky bit was a rather long "what if this number here" chain. Once one number could be discarded, everything else fell into place with no special tricks needed. But thank you anyway for the challenge. It is appreciated.
You can logically solve these puzzles without guessing.
You're right.