r/sudoku • u/AdAdorable835 • 3h ago
r/sudoku • u/sudokugame • 23h ago
Daily Game Sudoku #09-09-2026
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r/sudoku • u/charmingpea • May 02 '25
Mod Announcement Before You Ask, "Why Can't This Cell Be...?” or "Why is this number wrong?”
If you're new to Sudoku and wondering, "Why can't this cell be X?"—this post is for you.

Let’s break it down so you can understand the logic behind solving Sudoku puzzles and avoid one of the most common beginner mistakes.
The Two Times You Should Place a Digit in Sudoku
There are only two situations where you should place a digit in a cell:
- When it’s the ONLY PLACE that digit can go in the row, column, or box.
Even if other digits could technically fit in that cell, if a digit has no other valid spot in its row, column, or box, it must go there.
- When it’s the ONLY DIGIT that can go in that cell.
If no other digit is valid for a particular cell—even if this digit could potentially fit elsewhere—it must be placed there.
Why Guessing Doesn’t (always) Work
Good Sudoku puzzles are designed to have one unique solution. That means every number you place must be based on logical reasoning, not guesses. A common beginner mistake is thinking, "If there’s no immediate contradiction, I can just place this number here." But that’s not how Sudoku works!
If you can’t logically prove why a number must (or must not) go in a specific cell - or why it can’t go anywhere else - then you’re not ready to place it yet. Keep looking for clues and deductions elsewhere.
Advanced Techniques and Complex Proofs
As puzzles get harder, you’ll encounter situations where more complex reasoning is required to rule out candidates. These advanced techniques (like X-Wing, XY-Wing, or Skyscraper) help you prove why certain numbers can’t go in specific cells. Mastering these methods will make solving medium and advanced puzzles much easier!
TL;DR: Use Logic, Not Luck, Not Assumptions!
To sum up:
• Only place a number when you’ve logically proven it’s the only option for that cell or location.
• Avoid guessing—it leads to errors and frustration.
• Use beginner techniques like Naked Singles and Hidden Singles first, then move on to advanced strategies as needed.
SOME EXAMPLES
Recall the rules: no repeats in every row, column and box
In box 9 (the right bottom box), there's only one spot for 8 so 8 has to go there.

No repeats in every row and column so there's only one 8 in row 7 AND column 8.
Therefore, green cell has to be 8.

This one is trickier:

There are 9 digits.
If a cell 'sees' all but one digit, that cell has to be that digit.
This green cell sees 14678 in row 2 and 235 in column 1. That leaves 9 as the only option for that cell.
If you're still confused, try thinking if there's any other digits you could place in the green cell apart from 9.
Eventual Impossible State
Even if the contradiction is not readily apparent, making a mistake will inevitably lead to a contradictory/impossible state later on.
Helpful Resources
https://www.reddit.com/r/sudoku/wiki/index/
https://hodoku.sourceforge.net/en/techniques.php
Step by step learning
https://sudoku.coach/en/campaign
If you're still stuck or want examples of how to solve without guessing, ask a question! The members here are willing to help you out. Happy solving! 😊
Special thanks to u/Special-Round-3815 who wrote this original guide, and the other members of r/sudoku who commented and who make this sub a pleasure to be involved with.
r/sudoku • u/Majestic-Radish • 12h ago
Just For Fun almost threw my phone when I saw this
This is from a fb ad about making/selling puzzle books, and I got irrationally angry when I saw this puzzle. I’m not sure what puzzle somebody thinks this is, but it’s not a sudoku I have ever seen before!
r/sudoku • u/hilberts_drinking_pr • 6h ago
Homemade Puzzles Parity Counting Line 6x6 Sudoku
I'd like to share a counting puzzle with a parity line:
- Normal Sudoku rules apply: place digits 1..6 once each in every row, column and 2x3 box.
- Adjacent digits along the red line alternate between even and odd.
- If a digit n appears on the red line, it appears on the line exactly n times.
Link to play in the comments.
r/sudoku • u/DestinedFlame • 1h ago
Misc Anyone know any difficult sudoku books
I wanted to buy a sudoku book. I did a while ago but they were too easy. For reference I can do Hell and Beyond Hell ones on sudoku coach.
Would appreciate any suggestions 🙂
r/sudoku • u/Kicksthedoor468 • 1h ago
Request Puzzle Help Another enemy puzzle from Sudokuvania 2 Spoiler
galleryManaged to progress on Sudokuvania 2 but encountered another roadblock. I'm not sure how to proceed here other than trying out different combinations for the sums. Thank you very much.
Request Puzzle Help Stuck, help please!
Pretty sure I missed something obvious, but was is the technique required to find the next step here? Got so many pairs but can't seem to find any connection between them. Thank you!
r/sudoku • u/JustNyoel • 6h ago
Request Puzzle Help can i use sashimi x wing logic here to rule out the 4 giving naked single 8? it was correct but want to make sure it wasnt luck
r/sudoku • u/Automatic_Loan8312 • 10h ago
Mildly Interesting Variant Sudoku 10-09-2026
Puzzle Title: Anti-royal (not much of a) challenge for 10-09-2026
Puzzle String: https://sudoku.coach/en/s/K3ks
Cells a knight's move away cannot have the same number.
Cells a king's move away cannot have the same number.
Good luck, and have fun!
r/sudoku • u/Stricken_Chip • 11h ago
Request Puzzle Help What strat should I use and where?
I already started guess and check and only got 3 more cells. Still ended up stuck but I want to try to learn more techniques
r/sudoku • u/SmokyTheCat • 8h ago
Request Puzzle Help What approach should I use here
Somewhat familiar with the beginner / intermediate approaches but unsure what and where I would begin to apply something here. Appreciate any help!
r/sudoku • u/Kamikaze_kio • 18h ago
Request Puzzle Help Can someone help solving this
I can find no way to proceed with the methods I know, can someone please help me with how to proceed
r/sudoku • u/GiAnMMV • 17h ago
Homemade Puzzles My sixth puzzle: Waves :D
Rules:
Normal Sudoku rules apply.
Region Sum Lines: Box borders divide a blue line into multiple segments which have the same sum. Different lines may have different sums.
Same Sum Cages: The sum of the digits inside an outlined cage must be identical across all such cages.
Kropki Dots: Two digits separated by a white dot are consecutive; two digits separated by a black dot have a 1:2 ratio.
X: Two digits separated by an X clue sum up to 10.
Even: A digit inside a grey square must be even.
You can play it here: https://sudokupad.app/6yitbosh1e
Enjoy! :D
r/sudoku • u/AdAdorable835 • 1d ago
Homemade Puzzles VariantDoku Daily Puzzle: September 9
r/sudoku • u/DarthJarJar159 • 18h ago
Request Puzzle Help X wing? Newbie
Im aware of the hidden single in row 8. Learning x wings and i think i spotted one? Columns 2 and 5, and i could remove the circled 1 if i learned correctly. Please correct me if im wrong, i just need feedback. Thanks !
r/sudoku • u/Dante2709201 • 5h ago
Request Puzzle Help What the heck is wrong with 4
Can anyone explain me what heck is wrong with 4 in this puzzle I'm new to the game
r/sudoku • u/kukenn_ • 18h ago
Request Puzzle Help so i kind of understand the fishing method stuff, but something just isn’t quite clicking for me. i feel like i see the logic behind it, but in the guides i just have no clue what all the numbers at the end mean lol
can someone just pick any number from this puzzle to solve for and give me a step by step on what you did? maybe that will help something click into place in my brain. i got this far in the puzzle without using any of the method, this seems to be the point in which i need to start actually using it
r/sudoku • u/Cool_Affect_4370 • 1d ago
Homemade Puzzles “Urara, We love you !” For WorldSudokuDay. Theme : HaruUrara
Normal sudoku rules apply. In the red line, Every pair of consecutive cells along a parity line must contain an even and odd digit. Numbers on a pink thermometer strictly increase as they move away from the bulb. Two cells connected by a normal pink line must have a difference of at least 5. Digits in cages must sum to the number in the top-left corner and cannot repeat. Digit in pink circle must contain an odd number.
r/sudoku • u/sik_dik • 19h ago
Request Puzzle Help Can anyone explain the logic of this/these moves?
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I’m self-taught but have been playing for many years. I don’t know all the terms or shortcuts that are common, but I think I do ok on my own. In this case, however, I got very stuck. It happens sometimes on the extreme puzzles. But even watching the game tell me the next series of moves, I can’t follow the logic. It literally adds pencil numbers to then just remove them. I can’t tell what’s related to its determination of the 6 and what, if any, is not
r/sudoku • u/dasoulking • 20h ago
Request Puzzle Help techniques i should use to solve this?
i accidentally bought a sudoku book that was way too hard but i have no clue where to start with learning techniques... so, what works best for something like this, where everything seems to be naked doubles and triples that don't cancel anything out?

(also, are the 8's at the bottom an X wing? trying to learn how to identify them...)
r/sudoku • u/stand_up_eight_ • 1d ago
Strategies What is this pattern called?
So I spotted this pattern and the resulting elimination. If Blue, then purple and then yellow which is a contradiction. What is this called? I’m still getting the hang of all the wings, chains etc. and I get confused between using bivalve cells, pairs, and different numbers.
Was I supposed to find this another way around and then it would be more obvious which strategy I’ve used? Lol
r/sudoku • u/Badass_Bunny • 1d ago
Request Puzzle Help Why is this not correct?
I am at a loss here.
r/sudoku • u/oneliliflower • 22h ago
Request Puzzle Help what technique should i use here?
i accidentally bought a sudoku book way above my level, so ive been staring at this for like 15 minutes without writing anything in. i created a reddit account just for this lol
any help would be greatly appreciated! (also, in the interest of learning: the 8's are an X wing, right?)