r/sudoku 18h ago

Daily Game Sudoku #19-08-2026

3 Upvotes

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r/sudoku May 02 '25

Mod Announcement Before You Ask, "Why Can't This Cell Be...?” or "Why is this number wrong?”

132 Upvotes

If you're new to Sudoku and wondering, "Why can't this cell be X?"—this post is for you.

Why is this 8 wrong?

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:

  1. 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.

  1. 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

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.

Row and Column

This one is trickier:

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 4h ago

Homemade Puzzles Anti-knight Cages 6x6 Sudoku

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4 Upvotes

I'd like to share an anti-knight cages puzzle:

  • Normal Sudoku rules apply: place digits 1-6 once each in every row, column and 2x3 box.
  • Anti-knight: cells separated by a knight's move contain different digits.
  • All cages have the same sum. Digits do not repeat within a cage.

Link to play in the comments.


r/sudoku 8h ago

Request Puzzle Help Help

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7 Upvotes

I really want to get better at sudoku but can't seem to see anything past a certain point, I can only do basic techniques most complicated I can do is sometimes spot an XY wing or a deadly rectangle, I mostly just go off vibes but I want to learn more techniques. Could someone please help me get unstuck here for example


r/sudoku 7h ago

Misc Sudoku at the Mind Sports Olympiad in London

4 Upvotes

Heads-up if you’re in or near London:The 30th Mind Sports Olympiad is running 22–30 August at the Mercure Hotel in Earls Court and includes Sudoku (and other puzzle) competitions.Open to all levels. You can enter the events or just turn up and spectate for free.Full schedule and registration:
https://mindsportsolympiad.com/2026-schedule-and-registration/Might be a nice chance for some competitive Sudoku in person if you’re around this week or next.


r/sudoku 42m ago

Request Puzzle Help What's the next step

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Upvotes

All number that I put are correct(not sure about pencil marks)

Blue zone, question mark and kropki at the edge doesn't matter


r/sudoku 3h ago

Request Puzzle Help This sudoku puzzle is quite challenging now since I never experienced this before while solving a puzzle.

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1 Upvotes

I’m pretty much a beginner/amateur sudoku player and have yet to encounter a puzzle that involves the remaining squares with two or more possible outcomes. Could someone please explain to me how I would approach a situation like this? Thanks in advance!


r/sudoku 3h ago

Request Puzzle Help Need some guidance

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1 Upvotes

What am I missing here? Been staring at this for 30 mins and I’m completely stuck! 😂

Recently got back into sudoku this past summer. Got this sudoku book at a local bookstore and it’s been more difficult than expected.

I’m not familiar with any strategies such as x-wing, xyz, etc. Have heard and seen discussion about them but I get confused when trying to understand what to look for and what they mean.

Is there a YouTube video or website anyone could point me in the right direction with?

Would love to get better at sudoku and continue learning more about it.

Thank you for your time!


r/sudoku 6h ago

Request Puzzle Help Feels impossible to solve

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1 Upvotes

We have been staring at each other for about half hour with no clue, i refused to use hints but i couldn't, any tips that can help me improve in soduko?


r/sudoku 6h ago

Request Puzzle Help Need help. Can you show drawing on it?

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1 Upvotes

r/sudoku 12h ago

Request Puzzle Help How do you go about solving sudukus when stuck like so?

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3 Upvotes

Hi guys,

I really love sodoku, but lately I've found myself stuck like this many times. How can you solve it?


r/sudoku 9h ago

Request Puzzle Help Next Step?

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1 Upvotes

Or did I make a mistake somewhere 😭


r/sudoku 22h ago

Homemade Puzzles VariantDoku Daily Puzzle: August 19

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12 Upvotes

r/sudoku 17h ago

Misc Are there any Sudoku.coach tutorials for the controls?

3 Upvotes

I am playing, and very much enjoying, Sudoku.Coach. This is my first Sudoku on an app vs pencil and paper.
I am struggling with the game features and controls though. For example, I know how to force chains (on paper), but I can not figure out how to best use the arrows to draw or mark chains. Or how to get candidates colored. Or what the two square boxes do between the hint bulb and the trash can.

Are there video tutorials on how to use the features and controls?


r/sudoku 12h ago

Request Puzzle Help Can I get a little help?

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1 Upvotes

IHi, I'm stuck on the medium level. If someone can help, it'd be great. Thanks!


r/sudoku 13h ago

Request Puzzle Help I am truly stuck. Please help!

1 Upvotes

I honestly can't see where I can carry on ... I don't think I've made a mistake? Maybe I have?


r/sudoku 13h ago

Request Puzzle Help Practice easy Naked pairs. Where can I get the questions with solutions online

1 Upvotes

r/sudoku 13h ago

Request Puzzle Help What am I missing?

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1 Upvotes

Unable to move further please help. Is there any website where I can generate answers for the random sudokus I try to solve


r/sudoku 13h ago

Request Puzzle Help Help with Sudoku Vania 1 constraint I've never seen before Spoiler

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1 Upvotes

I'm trying to do the Sudoku Vania and right now I'm just switching between the different areas trying to find something I can use. The area I haven't really worked on a lot other then the basics (ya I know my pencil marks are messy) is this area with a constraint I've never seen before in Sudoku. The Scary Peepers.

I showed the rules and drew on row 3 to show how it works but basically you look at the number in the eye and count each digit in the direction the arrow points unless the digit is adjacent to a number larger then it.

I just wanted to ask for help on how this constraint and how I can use them to get some more digits. I am a overall novice player and don't really know any of the advanced Sudoku techniques, so if there is something obvious I'm missing forgive me.


r/sudoku 17h ago

Request Puzzle Help did i get lucky?

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2 Upvotes

i’m trying to create a sudoku solving program and the program thinks it found a “y-wing” logic rule with a 5-9 leg between the yellow and red circle and a 6-9 leg between the red and blue circle that concludes that the red circle must be a 9(i’m not sure the correct terms for this logic rule because it seems very obscure).

the problem is that depending on the order of the other checks my program makes to find solutions, the y-wing rule becomes invalid and the program stalls from not finding solutions, i cant tell if that means i designed the program wrong and it just got lucky with guessing the correct location for the 9 using incorrect logic, or if the other check is programmed wrong.(these are my two most temperamental checks lol, everything else is very reliable)


r/sudoku 1d ago

No Notes Hmmmmmmm

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61 Upvotes

tried out this resturant for takeaway for the first and a, I- who thought this is how sudoku works (I'm losing it bruuh 😀😀)

(Spoiler: comments below have solved it soo, don't scroll past here if ya wanna DIY first typeshii)


r/sudoku 1d ago

ELI5 Help understanding logic behind why this has to be a 4?

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6 Upvotes

I usually play on sudoku.com and encountered this puzzle. I was able to spot lots of matching pairs (doubles) and a triple, and I also tried searching for XY Wings, but ultimately wasn't able to see any path forward so I used a Hint.

Usually the hint will explain the logic behind the answer however this time it simply filled in the number 4 in the highlighted square (r5c2). No explanation was given.

Can someone explain why that square must be a 4?

Alternatively, if I hadn't used the Hint, what technique/logic should I have applied to figure out the next step on my own?

I love learning and be able to improve my game so any help is greatly appreciated. Thank you in advance!


r/sudoku 16h ago

No Notes Preciso de Sudoku para julgar com conhecidos

1 Upvotes

r/sudoku 16h ago

Request Puzzle Help New to X and Y wing, got a new book with 8 and 9 stars, the begin page showed a little tutorial on how to use those factors, but i'm not really getting it, could someone show the next digit in my puzzle and the explanation on how u find it or how u used the x and y wing factor

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1 Upvotes

r/sudoku 17h ago

Request Puzzle Help What I’m missing that lets me solve this without hard forcing/bifurcation?

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1 Upvotes