# Questions tagged [sudoku]

A Sudoku is a puzzle consisting of a grid to be filled with symbols, such that each constraining unit contains each symbol exactly once. The typical example is a 9x9 square to be filled with the numbers 1 to 9, where the constraining units are rows, columns, and 3x3 blocks.

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### All That Remains Sudoku

. 2 . | . 7 . | . . 9 . 9 8 | . . . | . . . 3 . . | 9 . . | . . . ---------+---------+-------- 2 . 7 | . . . | . . . . 1 5 | 7 . . | . . . . . . | 1 5 8 | . ...
533 views

### How to solve this Sudoku?

Here is the sudoku - I could think the following only. The top number box 3 coloumn wise should have some number - 6,7,3 (in some order). The box 3 column 2 -- 2,5,8 ( in some order), and box 3 ...
5k views

### Sudoku false positive (wrong move)

I'm new to Sudoku puzzles. I tried solving the one above but my last move was flagged as a wrong move(highlighted red). I believe it is a false positive since the $6$(highlighted red) I inserted is ...
268 views

### What is the maximum number of numbers a sudoku can have and have more than one solution?

I was watching this video where he talked about how scientists found the minimum number of numbers a Sudoku can have and still have exactly one solution. This led me to think of the opposite - what is ...
886 views

### What should be used to solve the next step of this sudoku puzzle

How to solve the next step in this sudoku ? I tried X-wing, hidden pairs and many other popular techniques found here http://hodoku.sourceforge.net/en/tech_hidden.php
526 views

### Was “Crook's algorithm” for Sudoku really only developed in the 21st century?

The following algorithm for simplifying (and very often completely solving) Sudoku puzzles: Label each cell with the set of all possible values it could take. Pick a row/column/block and for a value ...
364 views

### Do there exist Graeco-Latin Square style puzzles?

Sudoku, KenKen, and Skyscrapers are three examples of Latin square puzzles. In all three, players are challenged to complete a Latin Square, a NxN grid (typically 9x9) in which the numbers 1-N appear ...
2k views

### Hardest sum sudoku ever! (as well as how to solve them)

This sum sudoku is probably the hardest puzzle I've ever encountered, and I have made very little progress (a few cells or so). I found it in a book by Reader's Digest. The solution is given, but ...
3k views

### Is a 'legit' Sudoku puzzle supposed to be symmetrical?

Or phrased differently, are non-symmetrical Sudoku puzzles considered legal?
470 views

### Sudoku: Stuck, Need hint to move forward

I have applied the techniques I know to eliminate possible candidates. I'm stuck at this stage now, any hints to move forward are appreciated. I found this puzzle in Microsoft sudoku Android app.
1k views

### Why is the following 7 in Sudoku a mistake - Newbie

I'm a newbie at sudoku. Why is the following 7 in Sudoku a mistake?
201 views

### Finding a number in this sudoku

I have been trying this sudoku for nearly 5 hours now but im unable to find any number further...If anyone could help me out i would be really grateful.. Note: The numbers in black are the prefilled ...
3k views

### Do I need to guess from here on this sudoku?

I keep staring at this sudoku puzzle and can't seem to find the next move. Is the next move a guessing move? I thought sudoku always has clear solutions, you just need to figure them out.
1k views

### How to check a partial sudoku solution

John has started a sudoku puzzle and shows me his completed work, asking whether he's made any errors. There are no obvious errors (a number repeated in a row or subgrid). I know of two ways to ...
564 views

### Reasoning behind next step in sudoku

As you can see in the image, I've been struggling with this sudoku for quite some time and I'm completely stuck. I'm sure I'm missing one standard trick which would make it easy to solve, but I can't ...
163 views

### How to test a sudoku solver?

I have created a standard sudoku solver using my own algorithm. It relies on a continuous scanning with occasional tuple/pair searching. I am looking forward to test if this works properly. I have ...
142 views

### What technique I should use now? [closed]

I am stuck here. I don't want solution for this, I just want to know the name of technique which will be used here to go ahead.
276 views

### Can you help me with a logic to solve this puzzle?

I know the concept of pairing and removed pairs but what other concepts should I use to solve this?
205 views

### Sudoku: need a traceable hint for the next number

Partially solved sudoku: ...
137 views

### Smudged Sudoku - help me solve it!

One late evening I was making my sudoku. I finally finished until water spilled all over the middle-right block. The only thing I remember is the numbers present in the block (but not their position):...
140 views

### Sudoku, unclear next logical step?

Solved up until here, I took the sudoku through an online solver and it seemed to use a guess and check strategy? Is that the only way of getting the solution or am I missing something?
367 views

### Is solving a puzzle using uniqueness invalid? [duplicate]

(I don't know if this is appropriate to ask here, since it's a bit of a soft question about puzzles, rather than a puzzle itself. I'm not certain about the tags either.) When I was first introduced ...
214 views

### Trying to build a sudoku related puzzle box, struggling to ensure that there's only one solution

I want to build a specific puzzle box. The physical side I have down, but I'm struggling with ensuring that there's only one valid solution. The box consists of 9 freely rotating bands, inscribed ...
292 views

### What is guessing? [closed]

The whole difficulty of solving puzzles like sudoku is doing it without guessing. Well, either without any guessing whatsoever or with little enough that a human can still make retractions and come to ...
771 views

### Empty Rectangles - Does the rule apply when the intersection takes place inside the box with the empty rectangle?

The Empty Rectangles method is a strategy for solving Sudoku puzzles. I have seen the description of this strategy here, I have the following question: Is there a problem if the other end of the ...
264 views

### Does “naked set” method always solve a sudoku?

Is always possible to solve a sudoku (that has a unique solution) using only naked pair/triple/quad methods? If not, what about using naked set and hidden set methods combined togheter? I need to know ...
2k views

### is there any sudoku puzzle combined with magic square?

As everyone know in Sudoku sum of each row and column is 45. so all Sudoku solutions are some kind of magic square. but my question is: Have anyone seen a Sudoku puzzle combined with the magic ...
5k views

### Examples of sudokus with two solutions [duplicate]

I need some examples of sudokus having more than one solution. Do these puzzles have any common things?
422 views

### Another Determinant Sudoku

sudoku-determinant have been described well here : The Determinant Sudoku I have created another one. Number in the center is the value of the determinant Numbers 0 to 10 are the values of the ...
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### How to generate and count the 7x7 Latin squares

How many 7 by 7 Latin squares are there, and how can one generate examples of them? I am working on classes for a game, and typing in numbers manually from 1-7 in rows and columns from scratch is ...
395 views

### Help with a sudoku puzzle

I would really appreciate some help because I spent more than hours finding another number. It is supposed to be a very hard one but I started well and according to the key, my numbers are correct. Do ...
118 views

### What patterns could be applied in order to solve a Sudoku?

Related to this Q&A. I am looking for a pattern that could be applied in order to solve this Sudoku. The current patterns that I apply: Ensure that every digit appears once in every block Ensure ...
140 views

### Excluding number in a sudoku scheme

I have the following scheme: Please look at the lower left subgrid. The 8 may go in R7C1 or R9C1. If I put the 8 in R7C1 I'd have a 4 in R9C7 and a 5 in R8C7 If I put the 8 in R9C1 I'd have the ...
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### What is the best way to solve this 6x6 sudoku? [closed]

I eventually used a trial and error method to solve it: Assume B1 = 2 C2 and F1 = 4 C3 = 2 F3 = 6 There are no candidates left for A3 This let me set B1 = 4 and hence solve the puzzle. But is there ...
202 views

### Stuck on this Sudoku!

I have tried every trick I can think of... where am I going wrong?
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### Why is this Sudoku Skyscraper Failing?

I'm attempting to write a program that solves Sudoku puzzles using a variety of techniques. Up this point, I've only implemented naked singles and hidden singles (for rows and columns). I've been ...
265 views

### Non-Diagonal Pointing Problem

You can see the rules for pointing problem at this article. It has been clarified that there is no solution to this question. But, what if we remove the diagonal rule? is there any solution?
113 views

### stucked really bad with sudoku puzzle

Stuck with this for long time now, I have tried all the techniques yhat I know
270 views

### How many unique “miracle sudokus” are there?

The following "Miracle Sudoku" puzzle contains only two starting numbers, plus some additional rules that end up revealing the whole board: https://www.youtube.com/watch?v=yKf9aUIxdb4 (or Sudoku ...
186 views

### Can I swap two “yellow” corners on the same side?

The bottom two layers are solved, and the cross has been formed on the bottom layer. I am putting the corners in, ready to orientate them correctly, but I have two corners which need swapping. (The ...
129 views

### What am I missing in this Sudoku?

I think I am missing something in the instance below, since I could solve it only with a long-winded chain of deductions starting with the assumption that (coordinates are (row,column)): and ...
474 views

### An enigmatic sudoku

I entered the dungeon through a small, dark tunnel. After a seemingly endless walk I finally reached a small room. At the other side of the room, there was a big iron door. And in front of the door, ...
837 views

### What is a good notation for trial-and-error when solving Sudoku on paper?

When solving Sudoku on paper, I sometimes get to the point where I need to resort to guessing or bifurcation. At that point, I might guess one number, and continue solving, changing that guess if I ...
178 views

### What do you get when you mix a crossword and a sudoku?

For this CrosSudoku puzzle you must completely solve the sudoku grid below. To start the sudoku you must first figure out the crossword clues to get the starting numbers. Clue notation: x and y are ...
823 views

### Unsolvable sudoku net with maximum blocks

Definitions For a $9\times9$ grid $G$ (not necessarily respecting sudoku rules), a subset of cells $S$ is defined to be sudoku-friendly if the values in $S$ do not contradict the rules of sudoku. ...
67 views

### Setka - Complete grid using clues and sudoku-style logic; Theme - Fear Itself

This is a Setka puzzle; you can find more (along with a more detailed explanation of the rules) at our website, linked from our profile. Theme: Fear Itself How to play Setka, the short version: ...
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### What is the technique I should use now to go ahead?

This is a partially filled sudoku from the Sudoku Expert app. I thought I learnt all tricks and techniques. But clearly there is something I don't know about.
245 views

### Minimum amount of clues for a 16x16 sudoku

I know that 17 is the minimum for a standard 9x9 (3x3 squares), but what about a 16x16 (4x4 squares) sudoku?