Create a Sudoku Solver In Java In 20 Minutes - Full Tutorial

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Source code here: www.codingwithjohn.com/sudoku...
Let's create a Sudoku solver in Java!
Sudoku is a logic game, where you fill in numbers from 1-9 in a 9x9 grid. In Sudoku, each row, column, and 3x3 sub-grid must contain all numbers from 1-9.
Solving Sudoku in Java seems like it could be complicated - and some of it certainly is! But I'll break down the Java program for solving Sudoku into more simple pieces that we'll code together.
Learn or improve your Java by watching it being coded live!
Hi, I'm John! I'm a Lead Java Software Engineer and I've been in the programming industry for more than a decade. I love sharing what I've learned over the years in a way that's understandable for all levels of Java developers.
Let me know what else you'd like to see!
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[@19joni69]

Making a sudoku solver was actually the very first project I programmed once I'd learned the basics. This takes me back.

[@yahia1355]

Wow ! I have been coding for arround 5 years and could'nt come up with a solution!

[@19joni69]

@@yahia1355 oh I didn't do anything smart. I literally brute forced a solution. Basically going over every single square and trying the first number that works, then if I got to one that had no possible correct number I would go back until the first square that I could have put a different number in and tried the different number. Do that until you can fill every square correctly. Just literally trying every combination until it works. There are much better ways to solve this. But the not so smart solution works.

[@user-cg4vi4kn4v]

@@19joni69 🤣🤣😂

[@clo-1588]

You're an excellent teacher, John. I find your videos not only extremely helpful, but impressively well-made - and it's not even so much about the format (which is ideal), but the way you teach and the examples you give. You explain things in a logical, progressive way, and you're excellent at providing the right level of exposure. I do wish there were more teachers like you in universities - but then, we might not have you on KZbin ;) Please keep going with these tutorials, you are contributing to the community in a huge way.

[@stormybear4986]

This was, legitimately, the most interesting java tutorial I've seen in years! EXCELLENT!!!!!

[@janekk3397]

I'm so glad channels like this one exist. It was a part of my project and I would've never figured that out myself...

[@saviobatista9619]

Thank you! Amazing video, where I work I tried several times create something to solve our work schedule with some kind of algorithm but always fail, this was just exactly what I needed and hope to solve my needs. Thank you!

[@navyathamarreddy2807]

very nicely explained John, I saw few other videos as well for Sudoku Solver, but this is amazing!

[@nikhilraov100]

This program works perfectly. What a flawless algorithm you have written .

[@olayiwolaakinnagbe676]

This is the best video I found online for this problem. You are a great teacher, thank you.

[@rajeshg3570]

This is excellent .. i simply love the naming conventions of the vars..which makes its easy to read and understand the logic

[@mdrwsh]

it is amazing to see various algorithms that be used to solve sudoku, i made one but using while loop

[@krishnawadhwani5393]

I had recently discovered this channel, haha, and I started to watch your videos on TV Like I am watching some movies or some kind of entertainment, nice videos keep it up, subscribed after watching 2-3 videos

[@MykhailoZubanych]

Same)

[@jagi7976]

It’s beautiful when something that’s educational is also entertaining

[@abdurrouf4159]

You just nailed it. Mind blowing tutorial, no doubt.

[@Nikolai4567]

I didn't think this solution would have an adequate time complexity. Thanks!

[@zimbabwe8189]

Great video, your explanation was pretty clear!

[@penguin7863]

Sir before I watch your video I was a student who was struggling to solve recursion problems for my upcoming test. Now I get the idea about how to backtrack in recursion :) Huge thanks from South Korean student!

[@qurdedu4032]

Great explanation and great mini project Thank you so much. Looking for more project like this

[@carlostitlan]

Your explanaition is soo cool! You even make feel this stuff is easy.

[@staceyonuora5329]

Great video, I really enjoyed your explanation. Super thanks, this was very helpful

[@michaelkraemerman2009]

This was such a good explanation!!! I feel a lot more confident about implementing this. Also thanks for not acting like this is easy/obvious👏

[@sharadgupta8576]

It was just really awesome and in so nice way u described it's just really wow... M so surprised why just so less likes I have watched couple of videos before but u just explained really understanding with gotcha learn some new concept as well successfully found my final year project as well thanks for making this video... I will surely check out your more videos.. Great job 👍

[@guidopiotrowski7900]

Thanks for the great explanation! Keep it up with the channel!

[@tonyz2203]

OMG, I understand how to solve this complex problem now. Thank you so much!

[@sigfigronath]

This was really nice, fun and informative!

[@ulyses1018]

Great video! Thanks for this kind of tutorials John! :D

[@francescopiazza4882]

Great coding John! I got a "Hard Sudoku" solved in a few ms !

[@abidoyevictor2780]

Well explained! Thanks John

[@siddhantanand5751]

Hey, John I loved the way you went forward with explaining the video , you made it quite easy to learn the algorithm and fun too, i was curious if we can attach some image recognition tools like OpenCV etc for Java , so that we can scan a sudoku at run time and give an image back? I would love if you could show us how to do this if you like the idea.

[@Garrison86]

Amazing! Thanks for this, this helps me stay engaged in java

[@mthsffc]

This is exactly what I was looking for to complement my java studies. Projects with step-by-step explained. Please, keep it going, unfortunately here on KZbin, everything seems to be only JavaScript or Python. It would be great more projects with OOP.

[@jhuluan-jyun2594]

No wonder you’re a lead! Very clear sir, thank you

[@mira1m198]

Great explanation, easy to understand, even for beginners :-) Thanks!

[@vivekjj2986]

Thanks so much John. I spent a lot of time searching on youtube for a good tutorial on this. I wish yours was the first video so i could have saved time :(

[@ChristForAll-143]

Simply Nailed It, AWESOME EXPLANATION

[@Bury11]

cool project :) i'm fairly new to java, i programmed a small snake'ish game, so i understood the 2d array way better then i thought :D keep up the good work!

[@kunalkheeva]

How did you make it so simple, I always appreciate your content. your content is limited on youtube but whenever I get stuck in any problem and you have a video on that, which means, my last destiny is your video. Thank you

[@alzaeem79]

Beautifully well explained, thank you sir.

[@razvanungureanu8897]

I have reached the part where I didn't find a solution to erase the all the numbers of the board and to retry. I know it needed some recursion, but didn't figure out how. Your explanation was excellent and after reviewing your method, everything makes sense. Thanks and keep it up with these kind of videos!

[@jaydoshi5394]

Watching couple of videos from this channel every day in any order. But still makes sense

[@sritamabanerjee1331]

Loved your explanation..keep it up buddy 😊

[@josueramirez7247]

In an intro to programming textbook I own, it mentions in the preface that one difference from prior printings is that it removes the sudoku solver example code from the multidimensional arrays chapter because apparently is it too complex at that point.

[@PathWars]

Awesome, exactly the kind of KZbin channel I wanted: Regularly uploaded coding videos.

[@JonasKeil]

This tutorial is excellent John.

[@devoiddude]

Fantastic video and fantastic channel, your videos are great thanks .

[@kingsuley0581]

Loved this!

[@Daniel-iy1ed]

That was fantastic. Thanks 🙏

[@northnorth9913]

I like what you doing, Hope you get the chance to do Dijkstra’s algorithm, Time complexity and a few more interview related. I like your explanations

[@joekagerer]

I wrote a Sudoku solver in 2008 in Javascript, but it didn't quite use full recursion (my mistake) so it wouldn't solve moderately difficult puzzles. Mine includes character recognition of uploaded websuduko puzzles. This week I added "paste from clipboard" so that I didn't have to save/load my puzzle images. Today, following your model I finally got mine solving even the "evil" puzzles. Thank You John for this great lesson. Although now I don't feel that "I wrote the code", my page works and I did right the optical character recognition parts. I don't believe that I can share a link here, but I can try.

[@luigiq6429]

Great video John. Congrats on 500 subs!

[@CodingWithJohn]

Thanks!!

[@CodingWithJohn]

Well at least I've certainly gone well past 500

[@mastershonobi110]

Gr8 vid. Spent the last 2days working on this really breaking it down. I got a lot outta following and really understanding what’s going on here. Keep them coming…🙌🏿🙌🏿

[@javawocky]

Very nice. I do this stuff for fun. Recently did one of those word search generators which you see kids books all the time. Way more interesting to do than you may initially think.

[@joedevenski3291]

Fantastic stuff!

[@dunayqudretli3382]

Great tutorial !

[@AdamantlyAdams]

Bro, thank you for teaching. You are the go to guy!

[@footballalliance2412]

Hi John, i have learned a lot from your videos. I hope you won't stop making videos in upcoming days, it is really helpful for us. I can guarantee you will get a huge subscribers in coming days.

[@CodingWithJohn]

Thanks! Glad you're getting something out of them. I'll keep making them if people keep watching them!

[@estebanlegare]

Really helpful!

[@amaralensheriff]

As always, thank you John.

[@AkhtarReviews]

Loved it! 🔥

[@ponder2406]

Wow! That’s so cool! This was an awesome video! Very interesting :)

[@Gandobilis]

Very interesting tutorial!

[@nezetech]

Dude, thanks a lot!! You saved me

[@user-jh9ut7in8i]

like your explain!! very clear!!!!!

[@Darya-pu6ik]

its fantastic, i really like the way you teach, its intresting! However, could we do it using DP or is the an NP?

[@mynameispooop]

Awesome Tutorial

[@sanchitghai1455]

I like that you also play binding of issac 🙂. As for the program I loved it. It was well made video for beginners and one can't not understand the concept. Keep it up! 👍

[@b9944236]

Now I can solve it by myself, thanks a lot.

[@neeldiyora3575]

Excellent explanation 👏👏👏

[@surajverma-ut4kj]

Just one word for John 🙏🏼 Big ThankYou ❣️

[@user-sr7ht8rm6r]

John, thank you for everything! Could you maybe make a video on backtracking specificaly? That would be awesome! :)

[@rams2478]

WOW.. you are amazing....clean.. detailed.. explanation. Please do Leetcode problems also.. It will help us.

[@38YD]

love this!

[@manikandanm5567]

This is cool, thanks man

[@lukaskock7020]

Thank you very much!

[@danielmago4327]

amazing professor!

[@obitouchiha7545]

Wow sir you can explain things very well, let aside being multitasker.

[@strawberrykitty8337]

thank you so much!!!!!

[@JannisAdmek]

You teaching skills are really impressive, great work! I have one minor point to critique, you hardcoded GRID_SIZE 9 but used 3 as a magic number. You could have computed it once sqrt(GRID_SIZE) or just declared it as a constant.

[@Michael-se7ny]

sqrt(GRID_SIZE) would make no sense at all

[@JannisAdmek]

@@Michael-se7ny Really? Doesn't a Sudoku box always have side length of sqrt(GRID_SIZE)? But I guess the really clean way would be to define the sudoku in terms of the BOX_SIZE, since GRID_SIZE has to be square number. so a normal sudoku is BOX_SIZE = 3. (GRID_SIZE = BOX_SIZE * BOX_SIZE)

[@p_varma17]

@@JannisAdmek right

[@Pennervomland]

I‘d love to see this exact algorithm but more efficient. Knuths Algorithm X for sudoku sounds very interesting and shows a pretty good method for backtracking. I‘m too dumb to understand how to implement it in java but it could be a cool challenge for you.

[@stephanc7192]

You make truly great videos

[@cptsalazar4986]

Awesome johnny...

[@techtonight882]

I think we can use dynamic programming too, to reduce some of the complexity. We can use a HashMap to store if a number at particular position was a valid placement or not.

[@kesarscorpio]

i guess this one is for beginners and that's why he chose this way of doing it

[@cs0576]

But that is dependent on the previous placements. So I do not immediately see how that improves this algorithm.

[@smrtfasizmu6161]

The argument of the hashmap needs to be both the board and the placement of the number. How does backtracking in your algorithm work? I am not sure how you intended to do it with hashmaps and make the code less complex than what you saw in this video. Can you elaborate further? One idea popped up in my mind, but it is more or less a copy of what you saw in the video but without recursion. First you have an array which holds the position which are given in the beginning. Then, you proceed filling in the board and every time you find out that you can't continue filling in the board you backtrack the i and j variables of the loop until you reach the next number which you filled in and continue trying filling it after setting number To Try to be 1+the previous numberToTry.

[@mr.mirror1213]

iirc the whole problem is a system of linear equation , and u can solve it in O(n) if u use multigrid method

[@buddybuythis3889]

Wow! Sooo nice and free! Instant sub and hooked. Binge time.

[@nagasivakrishna5660]

wow,next level explanation

[@GeorgeVrachliotis]

Brilliant!

[@mohammadsadrayeganehfaal2323]

such a enjoyable algorithm!!!

[@djneils100]

this is a quality tutorial

[@NiklasEngelLive]

I user "Thread.sleep(50);" with try and catch to print all numbers one by one. But now I also try to avoid this step for the part where I want to print the default grid with the zeros. Thanks for the Idea and I will play with it a little longer :)

[@manusoftar]

I think that those nested for loops on the solve method are unecesary, you could add two additional params to send the current row and column and inside the function you just would need to either add the the rows or to the column depending on what you are doing... yes you will have to put some IF's, but the way you did it I think it will do unnecesary iterations, I mean, the last recursive call on a solvable board will put the needed number but there's nothing that would stop the initial call to the solve method from stopping it's iterations. Actually, on each recursive call it will have to traverse as far as possible on the board until sending back a false or a true if solved. You don't need the algorithm to traverse almost the whole board on each recursive call, you just need it to make a single step on the board instead.

[@sweetysojrani9323]

Awesome algorithm. It would be nice, if you could also explain the time complexity of the algorithm in your video.

[@samuelnilsson5505]

Love this

[@RomualdBrunet]

Using static methods and passing the board as parameter hurts my brain for some reason (vs using the board as an instance of a class)

[@ae6072]

same! Why doesnt he use the board as an instance? Is there any special reason for this?

[@Kanha0321]

Its amazing ❤️

[@rakeshreddypallepati6845]

Awesome Explanation......does the time complexity is ignored here as we are looping for a constant no of elements

[@abubakaradamu6278]

I think, i just found my best youtuber. Keep up the good work John.

[@patrickbradley4948]

Same

[@shintaromidorima1552]

it is 100% working teacher john and thank you for the source code

[@codegeek8256]

Please make a video on the Hand Of Poker (Poker Hands) Game, it seems to be used alot on interview assessments this days. I am sure alot of people need it.

[@jamesdepoorter726]

Hello John, why didn't you use TDD in this example? This could be a nice addition, because it constantly keeps the code in check

[@pratikdhargalkar4876]

Subscribed !!

[@wombozombo]

Fun way to learn about recursion 👍

[@widearchshark3981]

Good video. I think you could have explained that some cells could contain more than one number. It might seem initially that sudoku boards have just one option per cell, which made the recursion discussion confusing... Maybe! Nice though, thank you.