Timeline for Sudoku Help: Hard
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| May 8, 2020 at 2:55 | comment | added | NotThatGuy | @JasonGoemaat It isn't hard to guess and then backtrack if it doesn't work. In fact, it's probably what one might expect a beginner to do when they get stuck. For the average person, it could in many cases be the long way around when they can't find the shorter but more complex way, so in that sense it could be considered a less advanced technique. It's just time consuming. | |
| May 8, 2020 at 1:34 | comment | added | Jason Goemaat | It's all about the level of reasoning required, there's no difference other than in difficulty. Do you want to only deal with naked subsets? Pointing pairs and triples? Hidden subsets? X-Wing, Sword and Jellyfish? XY-Wing or XYZ-Wing? The last several are hardly better than just guessing a chain... If you don't want to stick to easy puzzles, the more advanced techniques are required. | |
| May 8, 2020 at 0:33 | comment | added | NotThatGuy | @AlexanderJ93 Regardless of what you call it: In one case you can write down facts like "this is definitely 7, 8 or 9", and then use that fact, and other facts, to directly deduce or narrow down the value of other cells. In the other case you assume (or "guess") something like "this is 7" and if you run into a problem you know it's not 7. It's a direct proof versus a proof by contradiction. I wouldn't try to argue that it's invalid (proofs by contradiction are certainly valid proofs in mathematics and logic), but there is a clear difference and I just don't want that in my puzzles. | |
| May 7, 2020 at 20:23 | comment | added | Rand al'Thor | @AndrewSavinykh The proof is in the penultimate paragraph of that answer, and applies to any kind of logical deduction puzzle. | |
| May 7, 2020 at 20:11 | comment | added | Andrew Savinykh | This link "always logically be solved without resorting to such logic" does not give any proof it just states it as given, also the question there is not about sudoku. Is there any indication that this statement hold true for sudoku? | |
| May 7, 2020 at 19:46 | vote | accept | infinitezero | ||
| May 7, 2020 at 19:02 | comment | added | infinitezero | This now turned into semantics. I think it's clear enough, what I mean. | |
| May 7, 2020 at 18:57 | comment | added | ryanyuyu | @infinitezero I see no distinction in "trying" from the "logic". If a column has all the values filled out except the last, how do you fill in the final cell if not by trying 9 possibilities, discovering that 8 of them lead to contradictions with the game rules and then concluding through a process of elimination that the 9th cell must be that value? | |
| May 7, 2020 at 16:58 | comment | added | Alex Jones | How does deduction differ from trying? I think a valid deduction would be something like "if I put a 7 here, then this one must be an 8 or a 9, but if it's 8 then there's no solution over here and if it's 9 then there's no solution over there, therefore this can't be a 7", but that's literally just trying. Maybe the difference is that you didn't write it down? | |
| May 7, 2020 at 16:00 | comment | added | infinitezero | Sure it does. By I prefer to solve by deduction rather than by trying. In theory I could just try any permutation of numbers and see if that leads to a valid solution or contradiction. | |
| May 7, 2020 at 15:53 | comment | added | Rand al'Thor | @infinitezero Well, it's up to you whether you like this method or not. But it's definitely logically correct, and guarantees an answer even when a uniqueness argument like Glorfindel's doesn't work. | |
| May 7, 2020 at 15:47 | comment | added | infinitezero | I agree with your reasoning. But I don't find this approach satisfactional :) | |
| May 7, 2020 at 14:50 | comment | added | Rand al'Thor | @infinitezero This is pure logic: you guess one of two possible options and then reach a contradiction, which proves that option logically impossible and so it MUST be the other option instead. It's a common technique in Sudoku and other grid-deduction puzzles. If you get stuck, try something (especially something unlikely) and see if you get a contradiction, which then enables you to proceed logically from the place where you got stuck. | |
| May 7, 2020 at 14:45 | comment | added | infinitezero | While I appreciate the answer (+1), this seems more like an educated guess than logic. | |
| May 7, 2020 at 14:01 | history | answered | Rand al'Thor | CC BY-SA 4.0 |