Sudoku. Lesson 24 When all else fails #1. Using a matching pair 

Having done that, the rest of the puzzle drops out quite nicely without any guessing.

Well done. The logic goes like this" if all small bumbers are correct if one number doesn't work then the other number will. Remember this qs aimed at teaching a technique. Thanks however for your imput.

So glad you found my site."the most popular site on line to learn sudoku" Please tell others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step how to solve. You can view all of my videos here: ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0w

Thank you Israil for your encouragement. You made my day. I suggest you look at the tutorials to learn more about sudoku. s://ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0wplaylists There are many different grids available for sudoku playing as well, and these different grid patterns ensure you have to use a different thinking process. Purchase a book which has a variety of grid patterns.

+Nick K I agree, I was very disappointed with the camera work, but couldnt afford to repeat the filming.

Yes your are right I missed some tricks but that can happen to all of us, however I was using this video to show a technique. The logic goes like this. "If not this then it must be that."

Mr. Anonymous It seems you do not understand how hard sudoku works, especially machine generated puzzles. Very often, the only way to actually solve the puzzle is via bifurcation. Trial and error is completely necessary for the same reason that proof by contradictions are necessary in mathematics.

Thank you Melanie, Now you are ready to look at the tutorials which I upload every month. The 12 tutorials will help you I am sure. ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0w

Sudoku Guy Hello Robin, Thank you but I can't upload your link. There is a mistake I think. Have a nice day. Melanie from the Netherlands.

Hi Raghu. There are many more ways to solve. Please look at tutorials from #20 and up. Have fun as you learn new techniques ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0w

You are exactly right. There are many ways to cook and egg. I went this route to show another way of solving. Yes this can be solved without using this method. Try not using a computer and see how you go.

Sudoku Guy Yes, I successfully solved yesterdays ZEIT-Sudoku. I just completed that from the ninth, I printed them out. But you could have chosen something that needed that method like like you did on episode 25.

You are doing very well. Please see my comments underneath the puzzle where I explain that the more techniques you know the more pathways you can take to solve

Wow, thank you! Happy greetings for the season. Stay safe.

Sorry I am not sure what you mean by a necked single. Study matching pairs as they are very important. Look at my site to find many tutorials and lessons on matching pairs. (see below) So glad you found my site." the most popular site online to learn sudoku" ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0w

@@SudokuGuy I am from India. I am a big fan of yours. I have watched many of your videos. That's what I wanted to say here. When you said in the beginning of this video that this Sudoku first is now stuck. There is no easy solution in sight. So I thought that digit 5 is present as a naked single in a cell R5C4 of block 5, then why should we use such a difficult method.

Yes See lesson 25

Sudoku Guy i have a competition tomorrow and i have seen your advanced lessons till the basics like capital t walking stick and those patterns plus tmb and lcr thats it nothing else but i am unable to find those patterns pretty fast. What would you advice it will be held in our school for the first time. Not officialy but a class wise! should i go with your method bcz at the end by using all trick i was unable to solve sudoko what should i do i hope you will help me

Good

!!!!!!

The difference between 'very hard' sudokus and the 'world's hardest' is so monumental it's disheartening. I just want to say that I solved the world's hardest sudoku, the right way, with logic.

Well done. so much depends on which algorithm is used.

Thanks for your comment. So glad you found my site."the most popular site on line to learn sudoku" Please share with others, subscribe and click the bell by the subscribe button. (It’s FREE) Have fun as you learn step by step how to solve. Below is my home page with all the videos listed. ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0w

+David Han You are right David, See my comments above in the general description.

pineapplewafers good point. The purist would say using "When all else fails" is a form of guessing based on "if one choice doens't work then the other will" providing you have all the small and big numbers correct. The purist would claim rightly that all puzzles (if genuine) should be able to be solved by logic..

Thank you for the clarification.

pineapplewafers The site I use (krazydad.com) has an "Insane" level that warns "They cannot be solved without making guesses". I would never actually try to solve these on my own, but they are 100% true sudokus, with 1 unique solution. That doesn't necessarily mean there are no logical techniques to be used, but that it is highly unlikely that a human could successfully use these techniques without computer aid. However, I have tried the level below Insane, "Super Tough", and I tend to use testing rather than straight "guessing and hoping for the best". What I mean is, you'll probably reach a point where you'll need to "let cell a equal 1", and see what that does to cells b, c, and d. Your hope in this test is to find either a contradiction (e.g. a row with two 1's), or an extra clue that lets you proceed logically. Now, this technique is not required on this video's puzzle, but as an example: On the top row of this puzzle, let the cell with "16" as candidates be a 6. Therefore, the 56 becomes a 5, and the 15 becomes a 1. That would force the 1 in the bottom-centre box to be in the same column as the cell that we let be a 6. And there's our extra clue: "If the 16 cell is a 1, the 17 cell below it must be a 7. However, if it is NOT a 1 (i.e. if it is a 6), then the 1 in that column must be in the 167 cell below it, therefore the 17 cell still cannot be a 1. The 17 cell must therefore be a 7." Here's the distinction though: in my example, you're not actually guessing that cell is a 6 - you're simply spotting a deduction based on "what would happen if it were a 6?" and showing that regardless of that cell's value, the 17 cell must be a 7.

+pineapplewafers I have just completed one which had stumped me by using this method.

+pineapplewafers This is basically forcing a chain. 3D Medusa Coloring will do this also.

They are coming. Check the latest tutorials. Go to playlists ru-vid.com/show-UCd8JaOdfEWcJOtwG6YayW0wplaylists

They are coming in future tutorials. I have much more to share. Thankyou for your patience.

Only one of them will work.

Hi Bruce, the logic goes like this " if one number doesn't work then the number will" providing you have put all the possible numbers in correctly.

Yes Martin you may think so. The logic goes like this. " if not this then it must be that"

Sorry Maste Recent tutorials are better.

It's not trial and error...it is called "if not this then it must be that".

ben dunn Logic doesn't care about whether you accept it or not. This is all about the fact that there do exist genuine, proper sudoku puzzles, a.k.a sudoku puzzles, which require extremely long and difficult-to-spot chains in order to be solved. Wing techniques will not help for those types of puzzles. As such, IF-THEN logic, a.k.a what you call trial-and-error, is completely necessary to solve those puzzles. You will never encounter a handcrafted puzzle with such an insane, tedious level of difficulty, but many machine-generated puzzles are impossible to find a solution to without this type of "guessing."