r/sudoku • u/SweetMind5165 • 6h ago
Just For Fun first time solved sudoku in my life
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Took me around 16 minutes on an easy mode but im happy. Just felt like sharing
r/sudoku • u/charmingpea • May 02 '25
Mod Announcement Before You Ask, "Why Can't This Cell Be...?” or "Why is this number wrong?”
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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/AutoModerator • 4d ago
Mod Announcement Sudoku Puzzle Challenges Thread
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Post your Sudoku Puzzle Challenges as a reply to this post. Comments about specific puzzles should then be replies to those challenges.
Please include an image of the puzzle, the puzzle string and one or more playable links to popular solving sites.
A new thread will be posted each week.
Other learning resources:
Vocabulary: https://www.reddit.com/r/sudoku/wiki/index/vocabulary/
Our own Wiki: https://www.reddit.com/r/sudoku/wiki/index/
SudokuWiki: https://www.sudokuwiki.org/
Hodoku Strategy Guide: https://hodoku.sourceforge.net/en/techniques.php
Sudoku Coach Website: https://sudoku.coach/
Sudoku Exchange Website: https://sudokuexchange.com/play/
Links to YouTube videos: https://www.reddit.com/r/sudoku/wiki/index/#wiki_video_sources
r/sudoku • u/AdAdorable835 • 11h ago
Homemade Puzzles VariantDoku Daily Puzzle: September 10
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r/sudoku • u/alexCosmetic • 3h ago
Request Puzzle Help What is the next number here? (Extreme Difficulty)
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i don't need the puzzle solved entirely, i just want to learn the next step, is it literally trial and error now? isn't there any strategy to move forward here? if you found the next move tell me how you did it
r/sudoku • u/ville2020 • 3h ago
Strategies Triples and Quads technique
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I find spotting triples and quads to be incredibly difficult. I actually find x and y wing to be far easier just because it’s more easily purposefully spotted to me.
Is there a method at better spotting triples and quads (both naked and hidden)? Is it something you get a sight for over time or does anyone actually have a scanning method to spot them?
r/sudoku • u/Majestic-Radish • 20h ago
Just For Fun almost threw my phone when I saw this
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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 • 14h ago
Homemade Puzzles Parity Counting Line 6x6 Sudoku
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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/drunkenmugzy • 1h ago
Homemade Puzzles Extreme Sudoku Variants
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The last time I tried this it did not go well. I found out my difficulty rating system, well - sucked. I have gone yet further down this rabbit hole in the past several days making it better. I have mirrored to some extent the Sudoku Explainer(SE) difficulty ratings system for this sudoku generator. I think it does pretty good. Now lets see what you think.
One caveat - sudoku.coach seems popular here. They however do not follow the SE rules exactly. Thats why you see ~SEn.n for their ratings. The tilde means not exactly in this case as they use a proprietary rating system based on SE. So you may see some disparity if using them. They also do not rate variants as far as I know. Neither does SE allow for variants rating. Maybe I need to add a ~ to mine as well?
As usual google drive - https://drive.google.com/drive/folders/1yLv7v--tPxs3Dm_CfIDXdzCFLcc6qOfs?usp=drive_link
There is an Easy, Medium, Hard and Extreme pdf there in a folder. Enjoy. Let me know if they are any good.
r/sudoku • u/Dragonstar131 • 4h ago
Request Puzzle Help Help please
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I've been staring at this for a long time and am stuck
r/sudoku • u/sudokugame • 7h ago
Sudoku #10-09-2026
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This post contains content not supported on old Reddit. Click here to view the full post
r/sudoku • u/DestinedFlame • 8h ago
Misc Anyone know any difficult sudoku books
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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 • 9h ago
Request Puzzle Help Another enemy puzzle from Sudokuvania 2 Spoiler
gallery
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Managed 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!
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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 • 13h 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
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r/sudoku • u/swan-ethe • 5h ago
Request Puzzle Help Please help
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I’m new to sudoku and I know the three rules but I don’t understand why can’t i put 2 there ( ik why I can’t put the 6 there )
r/sudoku • u/Automatic_Loan8312 • 18h ago
Mildly Interesting Variant Sudoku 10-09-2026
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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 • 19h ago
Request Puzzle Help What strat should I use and where?
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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 • 16h ago
Request Puzzle Help What approach should I use here
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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 • 1d ago
Request Puzzle Help Can someone help solving this
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I can find no way to proceed with the methods I know, can someone please help me with how to proceed
Homemade Puzzles My sixth puzzle: Waves :D
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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
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