Sudoku Solver

Button: Hint

Request a hint to find the next cell tosolve. A hint will either identify a cell which can be solved or a cellor cells where candidates can be removed. If candidates are entered onthe grid, those candidates will be used to help provide a hint,otherwise the solver will generate the candidates in the background.

Please Note: If the candidates entered arewrong or incomplete, the solver will not be able to provide a correcthint.

Since I first studied Sudoku in May 2005 I think I've finally got a handle on this puzzle. My original intention was to prove to myself that a small number of simple strategies existed that could solve every sudoku. How wrong I was. Sudoku has enormous depth and while this solver has grown up enough to crack 99.9% of puzzles there are many weird and wonderful examples that defeat it. The main reason to keep this solver in development is to analyse these difficult ones. To that end I've added new graphical tools and features which I hope you'll enjoy.

Sudoku Solver

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All feedback, comments, arguments, bug reports and strategy ideas are welcome. There is a FEEDBACK form with a column displaying comments and questions. Many thanks to all the people who have done so and helped improve this solver.

Many people have written to me to comment about multiple solutions for a given Sudoku. There are no logical tricks the solver can use to detect this other than to not complete correctly. The only way to check this is to perform a brute force analysis which tests every possible legal placement of a number. Computers are good at this and we now have a new yellow button called "Solution Count". Try this on any Sudoku to check whether it has a unique solution.

Take Step first displays the possibles or candidates for each unknown cell. These are the numbers that do not contradict any known or solved cells. Once these are displayed Take Step will step through other tests and then loop until it can go no further. The first few tests are the most productive and the solver will often loop between them. If any are successful and the board is changed in any way it will go back to the start and "Check for Solved cells". The reason for this step is to make it easier to spot what's changed. Many of the strategies have knock-on effects which means that they can't be run back-to-back - it's essential that we return to the basic steps. We go back because we want the easiest solve route.

To solve sudoku one doesn't require the knowledge of mathematics but require the logic and reasoning. Solving Sudoku Puzzles daily helps with your brain. It improves the concentration and logical thinking. One can look for sudoku puzzles given in Newspapers or can play them online provided by many websites.

This website anysudokusolver.com is a free online automatic sudoku solver that solves almost any sudoku puzzle in matter of second. It applies Javascript, Brute Force method and Dancing Links Algorithm for quick solution. Ever tried but stucked on sudoku puzzles given in newspapers, magazines and online. You can use Anysudosolver to get its solution instantly and move further. Do not use this sudoku solver tool without giving your best effort while solving the puzzle.

A lot of the short sudoku solvers just recursively try every possible legal number left until they have successfully filled the cells. I haven't taken this apart, but just skimming it, it looks like that's what it does.

The first thing that I did was continue my "easy" Sudoku solver's approach of finding the possible values for each square based on which values were already in that square's row, column, and box. I stored all of these values in a list so that I could quickly refer to them while backtracking or finding which value to use in that square.

Sometimes it just takes time and practice -- the Sudoku solver I spent countless college hours on took me less than an hour a few years later. I will say that computer science programs don't tend to start in a way that allows people who didn't write code earlier in life to participate, which in a few years with computer science education policy changes may be okay, but for now eliminates people who grew up in small towns, who weren't interested in coding growing up, or who went to weaker high schools. In part, this definitely contributes to the success of coding bootcamps which start with the fundamentals and teach the less conceptual web development skills rather than heavy algorithms.

I can now write the Sudoku solving algorithm, but I don't think its a necessary skill for developers to have -- I still was a successful software engineer shortly after the time period that I couldn't implement the Sudoku solver. I do think that some computer science fundamentals can be very helpful, even for new developers. For example, the concepts behind Big-O notation can be really helpful for deciding between approaches. That being said, most data structures and algorithms aren't used on a day to day basis, so why are they the basis for interviews and computer science classes instead of the more important things used every day?

Once I ran into your GitHub account and I saw the sudoku repo I didn't open it though because I don't like spoilers hahaha so I decided to make my own sudoku solver that like your first version only solve easy ones...I tested it using the Gnome sudoku from ubuntu 14.04 and It solves easy and medium level of difficultly this is the repo github.com/lmbarr/sudoku-solver

Nice job! Always rewarding to go back and solve problems that stumped in the past. You know... now that I think about it... I'm not sure I ever succeeded at writing a Sudoku solver ? Perhaps it's time to fix that for me, too!

Amazing, the sudoku part almost exactly mirrors my experience.

I first wrote it in javascript, with sets of possible numbers for every cell and human-like non-destructive transforms being applied (only answers we are sure about). There were quite a few different transforms, because I picked a modified version of Sudoku which had these additional blob sum constraints, which were interesting because they were indeed sums and not sets of the [1,9] range.

For the UI, it used Vue, but really the renderer was mostly handwritten svg. It solved the lesser difficulties, but then I got bored.

Later, I stumbled upon someone quoting the backtracking algorithm as described in wikipedia. So I implemented it in Rust, with the additional constraints. The first time I wrote it, it solved them all in negligible time. I also tried it 3x4 and 4x4 boards. 4x4 gave noticeable time, and anything above 4x4 took too long to run.

Perhaps applying human-like transforms is computationally valuable at bigger board sizes to reduce the iteration space dramatically.

Maybe I'll still port those, or make the rust code an API or a WASM embed to the UI. Probably not though.

Another one! I wasn't given a Sudoku solver to do as part of a class (I trained in engineering), but have done one recently simply because it's really interesting. Pretty sure this one is efficient (github.com/rantydave/sudoku), took a lot longer than a couple of hours :)

Not saying that the code is inefficient, but I've created an algorithm which will solve the sudoku puzzle like we humans do (i.e. there would be no hit and trial of numbers). I wanted to make my own sudoku puzzle and solve it, but the thing is I couldn't make the question set. Whenever my algorithm would finish placing the numbers, it always turned out that a number was present twice in its undesired area. Help anyone?

First of all, reduce is called which is the iterative step that removes impossible values based on the definite along with the rules of sudoku. We will get back to this function later on. As before, calling reduce might lead to three different cases:

I am going to try to take what I can from your blog and create a solver for str8ts ( ). Since this is a couple years old, is there anything that you would do different now from the time you wrote this?

A few months back I was in an hotel room at 4 am in the morning when the thermostat inexplicably decided to heat my room to 90 degrees Fahrenheit. That woke me up, and since I had nothing to do for a few hours I decided to write a Sudoku solver (because everyone has to write one).

I know Sudoku solvers are a bit CS 101, but perhaps it can at least illustrate that if you make some fairly minor performance considerations up front and throughout, you can get a reasonably fast solution from the start without having to jump throgh any crazy hoops, or even optimizing in any serious way at all.

;Hello everyone! I have been working on a huge project (atleast seems huge to me), almost all pieces polished, but i'm missing a sudoku solver. I'm already burnt out, getting sick by only looking at code. Was searching for some solvers on the internet written in au3, but i didin't find a single one that i could modify to be like this:

Building a Computer Vision (CV) Sudoku solver had been one of the projects I have wanted to do for fun. To build a Sudoku solver using CV, I had to first start from a base solver, and subsequently build the CV input, UI, and transition to a mobile form-factor.

After every board update, you call the solver module again with the updated board configuration, and it will try solving it from the new state until there are no more empty cells (meaning you have solved it since you reached all cells, and all entries had been valid - else you would have backtracked).

This will be an ongoing social experiment as I layer on new capabilities to build increasingly more complex solutions. This hopefully drives home the point that a previously acquired skill allows you to do more in the future. I have set a target to write base solvers for each of the Sudoku-variants below.

Some time ago, I got curious about building a "Sudoku Solver". At some point during my research, I had been experimenting with the Gurobi Optimizer to solve some problems I was facing. Some time later, I found PuLP, an open source solver for Linear Programs (LP), which allows for an easy solution to define and solve LP problems. Its tutorials include one in which a Sudoku Solver is built. By the time I learned about it, I had already built mine, and had already seen some other solvers, both downloadable and online. But I still have not seen any solvers for "Samurai Sudokus", so I built mine. And now, I have put it online. 2351a5e196