Okay, jumping in. Also, I don't have many ways to thank you for all the work you do so I am linking everyone who stumbles onto my RU-vid shorts on autism and sudoku, over here. 😊🤩 and i am off to video 53 😁
Thanks. The uniqueness techniques are what I would call the most advanced puzzle-solving techniques. The logic is somewhat peculiar. Here's a nice wiki page on the uniqueness techniques: hodoku.sourceforge.net/en/tech_ur.php
8:57 Correct me if I'm wrong but the pair 56 in R7C5 also determines a hidden rectangle on R79C58. R9C58 have a strong link on 6, one of them must be 6, and R79C8 also have strong link on 6, one of them must be 6.
Thanks for your video all most all unique rectangular type are cover and discuss this is helpful to solving a hard or expert sudoku my request in future also make video for all other types like avoidable and extend unique rectangular your explain method and example so good and nice easy able to understand thanks for your hard work and knowledge full video thanks from heart God bless you
Thank you for your friendly comments! Two more uniqueness videos to go. These are definitely some of the hardest of the advance techniques to learn and do videos on. I will be glad when they are over! There will be 10 uniqueness videos when I am done. The next two will be on "Avoidable Rectangles."
I have a question in your very first example at 1:00. I started working on the puzzle from the very beginning but I couldn't get to the stage in which the cell R4C5 contained only the candidates (2,4)? I got (2,4,9) but I couldn't get rid of the 9 to end up with (2,4) as the candidates so that I could use the hidden rectangle technique. Also for cell R6C2, I have the candidates (3,4,7,8) but I couldn't get to (3,7) at the stage of your example. Thank you very much.
You make a very good point. The example uses a 6-cell Sue de Coq to get to the point where you have a (2,4) in cell R4C5. Here's the solution path generated by the Hodoku solver: imgur.com/v9e1QTK But you are right that having a 6-cell Sue de Coq just before the Hidden Rectangle is probably a bad example. Finding a 6-cell Sue de Coq without software is practically impossible. If you want to generate your own practice exercises having a Hidden Rectangle, take a look at this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-jPssW_W3iH8.html Here's four practice exercises having Hidden Rectangles you might find more to your liking: imgur.com/LPu1rOT imgur.com/gUBjIT2 imgur.com/5WM6B2b imgur.com/OPXYBpJ Sorry about the bad example. Hopefully these 4 will help you.
At mark 5:50 you are saying: "...the four cells only occupy *at most* two blocks". Do you mean "occupy *exactly* two blocks" or is it possible to get whole hidden rectangle within a single block ?? 🤔
I had about a six month discussion on this topic with someone. There are two parts. First, if the pattern occurs within a single block, other simpler techniques can be used first. I always advocate that the 7-base techniques (Naked Single, Hidden Single, Naked Pair, Hidden Pair, Locked Candidates, Naked Triple, and X-Wing) always be used first before any advanced techniques. The 7-base techniques would clear off any candidates in a single block that might look like a rectangle issue. The second part, "occupy two blocks" is what the long discussion was about. The person I was talking with was using uniqueness techniques all over the place. Instead of just using a UR and four cells within one chute over two blocks, he would use them over two chutes and the four cells would be located in four separate blocks. It's kind of tricky to prove but what happens is because we have only 9 cells per house in a 9 x 9 grid, it is impossible for the UR situation to occur over four cells in four separate blocks. For a UR to occur over 4 separate blocks, you would need a 12 x 12 grid (I'm not sure of the exact size). It's important to understand the nature of a UR. When we use UR techniques, it's not a pattern. We are using the logic that is built on the assumption we have only one solution. So we lean on this assumption by eliminating the possibility of a puzzle having two solutions (because we know it can't). It's not normal Sudoku logic like you get with normal pattern technique. Here's a really good wiki page on UR and it also talks about the 2 x 2 x 2 rule: hodoku.sourceforge.net/en/tech_ur.php It says this: "A common mistake when looking for URs is to violate the "2 blocks" rule (see the Sudopedia article for an example)." Here's the article: www.sudopedia.org/wiki/Unique_Rectangle Its doesn't really say much. It's hard to show and prove. Last year was when I was studying this hard. As I said, when the 4 cells are in 4 blocks what happens is other techniques will eliminate UR candidates (because the grid is only 9 x 9) so then the UR is not a problem. I hope I explained this well. This is really tough question. You are will soon be the master showing me stuff!
I don't quite understand what you are asking. Are you suggesting there's some kind of HR with r1c9, r3c8, r5c8, and r5c9 ? What 4 cells are you are considering. I do see r1c9 and r5c9 forming a Naked Pair. But I'm not sure what you are implying what it means.
The uniqueness logic is a bit tricky. By leaving the possible 4 candidate in R6C3 could result in having multiple sets of Naked Pairs which would then cause two solutions. The way to think about this is if there is not a 6 in cell R4C3, and there is not a 6 or 8 in cell R6C3, and there is not a 9 in cell R6C6 then bad things happen. So we must conclude in the three cells just mentioned, one them MUST be set to a value other than 2 or 4. When we try all the possibilities, it turns out R6C3 can never have a value of 4. This is because the possible 2 candidate in cell R4C6 is participating in two Strong Link relationships with the 2 in cell R4C3 and the 2 in cell R6C6. If you are not familiar with the way links work in a Sudoku puzzle, take look at this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-cVwV3MXXx5c.html
