Table of Contents: The Problem Introduction 0:00 - 0:44 More Information On The Problem 0:44 - 1:52 The Brute Force Approach (Complete Search) 1:52 - 3:09 The Backtracking Approach (3 Keys To Backtracking) 3:09 - 3:30 Our Choice 3:30 - 4:18 Our Constraints 4:18 - 6:28 Our Goal 6:28 - 7:41 Time & Space Complexity 7:41 - 9:11 Conclusion 9:11 - 9:34 The code for this problem is in the description (with many comments for teaching purposes).

@raghavkakar8092

4 жыл бұрын

Where is the code in the desc?

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

@farahalaa2362

4 жыл бұрын

Hello, why the filling in empty spaces is row by row ?

@ostapo2888

4 жыл бұрын

​@@raghavkakar8092 here is the simplest solution using the approach from the video if you really need it - github.com/orishko-py/codewars/blob/master/sudoku-solver.py

@tanaygupta632

3 жыл бұрын

Where the fuck is code in description?

Hey bro, you are not yelling. I can feel a strong passion from your voice!

@BackToBackSWE

5 жыл бұрын

Nah...I'm yelling haha

@aayushsharma1452

3 жыл бұрын

@@BackToBackSWE no you are not

thank u so much!! but where's the code exactly?

very clear to illustrate the hard part of this problem. Great job man, you deserve more subs, and keep going!

@BackToBackSWE

5 жыл бұрын

thx

I was hoping you would do a dry run on the example input board, just like you do for most of your other videos. That really helps in firming the understanding, more than the code.

@BackToBackSWE

4 жыл бұрын

yeah

Great explanation. I've checked out a lot of your videos past few days. You are doing a great job. Wish my algorithms professor was like this.

@BackToBackSWE

4 жыл бұрын

thanks

Nice solution. I followed your approach but I did a bit of an update on it. Instead of checking everytime if a character can be placed in row or column or region at O(n^2) runtime, you can do that in constant time by saving keeping track of the content of each region, each row, and each column, then you can backtrack on it. after trying any character.

@BackToBackSWE

4 жыл бұрын

nice

If you keep this up, as you started at the very young age at college, I am sure you will go very far. :)

@BackToBackSWE

5 жыл бұрын

I will haha, this is the next launch twitter.com/thebigoguide, then I'll be back to tend to this channel

I love your videos. They are very helpful and you explain each problem clearly. Thanks

@BackToBackSWE

5 жыл бұрын

I love u

Excellent Explanation and it can be easily seen , the amount of effort you have done thanks a lot for this video

@BackToBackSWE

5 жыл бұрын

sure

U R A LEGEND ! KEEP IT UP 💪

@BackToBackSWE

4 жыл бұрын

no u

I actually prefer the yelling and passionate approach. You’re the best!

Thanks for the great explanation and clean code.You made my day.

@BackToBackSWE

5 жыл бұрын

nah, you made my day for watching

@sahiljindal3202

4 жыл бұрын

Mr. Nobody provide code to me too

I love your video. It's one half Sudoku tutorial and one half inspirational speech. Backtracking can solve many problems.

@BackToBackSWE

4 жыл бұрын

lmao, old video, apologies

@aidandanielski

4 жыл бұрын

@@BackToBackSWE Quality trumps age. (You know what I mean...) ;)

Where is the code?? There is NO code in the description!

Thanks for the video, it's good explanation. Can you make a video about 8 puzzle problems using backtracking, I really hope for it?

@BackToBackSWE

5 жыл бұрын

maybe? Technically I can only directly make videos requested by patrons but I'll consider it. (if someone sees this comment in 1-3 years and the Patreon doesn't exist ignore this)

Thanks a lot man, you're helping tons of people. Hope you have a great day

U aren't yelling this shows ur passion towards the problem don't change the tone

@BackToBackSWE

3 жыл бұрын

thanks haha

Hey thanks for the vid! I was looking over the code and the comments really help make everything clear but the one thing I didn’t get was in the valid char placement method when you check if its a valid placement in the region, the formula for int I,J and topLeftOfRow,Col how did you derive those?

@BackToBackSWE

5 жыл бұрын

int regionSize = (int) Math.sqrt(board.length); // gives us the size of a sub-box In a 9 x 9 board, we will have 9 sub boxes (3 rows of 3 sub-boxes). int I = row / regionSize; int J = col / regionSize; The "I" tells us that we are in the Ith sub-box row. (there are 3 sub-box rows) The "J" tells us that we are in the Jth sub-box column. (there are 3 sub-box columns) Integer properties will truncate the decimal place so we just know the sub-box number we are in. int topLeftOfBlockRow = regionSize * I; // the row of the top left of the block int topLeftOfBlockCol = regionSize * J; // the column of the tol left of the block That multiplication takes us to the EXACT top left of the sub-box. We keep the (row, col) of these values because it is important. It lets us traverse the sub-box with our double for loop. Each coordinate we touch will be found by an offset from topLeftOfBlockRow and topLeftOfBlockCol. For 20 minutes I debated what to name these things and I literally couldn't think of a very clear name so left them alone. The fact you had to ask this means the code is too opaque. It is my fault and I will rename things to make things more clear.

@airysm

5 жыл бұрын

Back To Back SWE no worries! Thanks for the explanation

bro you deserve million views and subscribers.thnk u!!

@BackToBackSWE

5 жыл бұрын

haha thanks

Loved it more when you are loud:) such energy is contagious!

cannot believe it, I first search Sudoku Solver in youtube, I did not found your video. Then I watch other guys video which make me confused but I saw a leetcode link under that video comments. Then in the leetcode discuss, I saw your video link, that's how I found it.

@BackToBackSWE

5 жыл бұрын

hahahahahaha, yeah, this channel is new and KZread thinks it sucks ass

Nice explanation, I find easier to understand the reasoning behind the approach

@BackToBackSWE

5 жыл бұрын

nice

I got this same question in an interview, and the problem I faced was in checking if placing an element breaks a sub grid or not (It's relatively easy to check rows and columns). I believe that's the only important thing missing in this video. Otherwise I'm a huge fan of your channel ❤️

@BackToBackSWE

4 жыл бұрын

thx

@ptronic

2 жыл бұрын

It's not hard if row between 1 and 3 and column between 1 and 3 subsection 1 etc

Great Explanation! Thank you Brother!

What happen when the program has picked a number for a cell and later needs to change it due to other cells constrains? I mean it could be valid at the time it picks a number but may need to be changed later?

@BackToBackSWE

4 жыл бұрын

Yes, if that is the case that choice will take us down a path that will hit a "dead end". We will backtrack to the same decision point and make the next decision from that same cell into a new path of exploration.

@matejriha4128

4 жыл бұрын

@@BackToBackSWE How do I locate the number which caused the problem?

One question I have is how we can figure out which valid value to use. For example, when we are looking at the second blank spot, you put a 2 there and proceed with the assumption that it is valid. However, how did you know that the second blank could not be a 6 instead. There are no 6's in that row, column, or sub-matrix?

@BackToBackSWE

5 жыл бұрын

When I place the 2 I just randomly choose that number, no methodology behind it. Check out the code in the description. What really happens is that we try numbers 1 to 9 using a for loop and if a placement ends up not working we backtrack and remove it from the board.

Wow.. brother thank you... You made this really easy

@BackToBackSWE

4 жыл бұрын

sure

thank you very much sir, very helpful

Thanks for your wonderful explanation sir..

It's always safe to like your video at the very start.

@BackToBackSWE

4 жыл бұрын

lol

Thank you guys this video helped me in my assignment Thank you again Where are you from guys?

@BackToBackSWE

4 жыл бұрын

maryland usa

Hey mate, love your videos, but I have a question about the line 35: board[row][col] = EMPTY_ENTRY; why does it work with it and why doesn't it work without it? I mean, you set a value for a cell, and then you set it to EMPTY_ENTRY, why?

@BackToBackSWE

4 жыл бұрын

Imagine what is really happening. It doesn't matter if clear it or not. The cell gets overwritten.

Such a simpler and great explaination....and u are not yelling man😆....thanks it was very helpful...👍

@BackToBackSWE

4 жыл бұрын

thanks, ok, and great

This is the third succesful classic algorithm I learnt from you. Absolutely love your way of teaching ^_^

@BackToBackSWE

3 жыл бұрын

great and thanks

@CodingWithPrakash_

3 жыл бұрын

kzread.info/dash/bejne/pH5tsKiEadbFnaw.html Valid Suduko (Explained like a champ)

I don't understand whats all the dislike..what amazing explanation. he basically told you the approach. the coding part is easy. the check if can place part is basically the previous question ValidSudoku. I actually prefer this kind tutorial rather that just given me the code upfront.

@BackToBackSWE

4 жыл бұрын

Hahah, the video's quality is kinda bad.

your explanation is best ,best teacher ever

@BackToBackSWE

3 жыл бұрын

thx

love you man!!

@BackToBackSWE

3 жыл бұрын

u 2

Great Video, Was just wondering where is the code...

@BackToBackSWE

4 жыл бұрын

thanks and the repository is deprecated - we only maintain backtobackswe.com now.

When did you actually explain backtracking though...

@BackToBackSWE

4 жыл бұрын

dont remeber this vid

@sharpnova2

3 жыл бұрын

he didn't at all. kind of weird. i clearly see how to solve this problem from what he did say but only because of my background

Hey bro thank you for your video. I couldn't get the code to look at how it was implemented

@BackToBackSWE

4 жыл бұрын

It is on my github but the repsoitory is deprecated

@kristianusifoh9307

4 жыл бұрын

Back To Back SWE ok thank you.

yeees, I am not a better person but I love your energy and now I know how to solve and that makes me a better engineer. Thank you! And please don't change your style.

@BackToBackSWE

2 жыл бұрын

Thank you, glad you liked it 😀 Do check out backtobackswe.com/platform/content and please recommend us to your family and friends 😀

Great! Thank you!

@BackToBackSWE

Жыл бұрын

glad it helped

What if in the middle of the grid validation check fails? What do you do then?

Man you are amazing!!

@BackToBackSWE

3 жыл бұрын

thanks - im normal

@CodingWithPrakash_

3 жыл бұрын

kzread.info/dash/bejne/pH5tsKiEadbFnaw.html Valid Suduko (Explained like a champ)

Nice video and great explanation. I have brought our course but all videos are not there, what I meant is that some videos that are there on youtube are not in the course. why so?

@BackToBackSWE

3 жыл бұрын

Hi! The intention is that some videos here are lower quality and don't explain the problem how I see it best explained. Also bad gear like microphone kept some videos out of the service as well tabled for a reshoot.

How i can apply vanilla backtracking on this problem for at-least 10 iterations

@BackToBackSWE

4 жыл бұрын

not sure

absolutely love the way you explain everything... has helped me a lot.

@BackToBackSWE

3 жыл бұрын

great!

Very clear.

Hmmm, am I the only one who can't find the code? He said that in the description box there is a link to the code

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

@SunFoxPL1

4 жыл бұрын

@@BackToBackSWE So if we want to see the code we need to pay? That's... really ugly. I mean it's really ugly marketing move.

@mangekostorm9211

4 жыл бұрын

@@SunFoxPL1 It's still on his github though it is no longer maintained. The solution is also available on a variety of other websites. It makes sense that you should pay for new content (and it's much cheaper compared to other coding schools) since he is taking so much time to prepare and constantly update the materials when he could be working a SWE job and making a SWE salary. We should be thankful that he still has his original videos up.

@SunFoxPL1

4 жыл бұрын

@@mangekostorm9211 Oh I don't mind him getting money for what he is doing, just the fact that he posts video on youtube which is just half done (there is no code, and when someone asks about the code he just says that you need to go to the webpage and pay) is very unprofessional.

@prinzuchoudhury6920

4 жыл бұрын

github.com/bephrem1/backtobackswe/blob/master/Dynamic%20Programming%2C%20Recursion%2C%20%26%20Backtracking/SudokuSolver/SudokuSolver.java

Hi Sri,I couldnt find your code in the description below.

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

This is brilliant. Thank you!

@BackToBackSWE

4 жыл бұрын

sure

1:04 Double "Our Choice" on screen ? :))

@BackToBackSWE

5 жыл бұрын

OOPSIE!

Being you answered all of the questions asked of you, I would like to know if I use a blank board how many different puzzles can I create? Your video is far beyond my comprehension so I will not say you are a poor teacher, but you are the first person to answer all of the questions on your site. I asked a relative that question (he had a doctors degree in math) and he did not or could not answer my question. I enjoy the puzzles but not as a math problem. For me that takes the fun out of the hobby.

@BackToBackSWE

4 жыл бұрын

How many different sudoku boards? Well, that's hard. The total invalid boards is 9*9*9*9*9*9*9*9*9*9*9...basically n^n which is 9^9 which is 387,420,489 boards. Valid boards? That is harder to count.

@chetthejet3896

4 жыл бұрын

​@@BackToBackSWE Thank you Bro. I figured you would give me a good answer.

@BackToBackSWE

4 жыл бұрын

@@chetthejet3896 lol, I try

One of the problems I'd have with this is that the 1 at the start might not be the correct answer. The first empty cell could be 1,2 or 4. You don't know which it will be until you solved a certain number of the rest of the puzzle. I'm guessing the code keeps passing thru, but while you're there you could just find ALL the answers the position could be before you move on. I get that 1 has a 1 in 3 chance of being correct, but I'm not sure if that's the best approach.

@BackToBackSWE

4 жыл бұрын

The backtracking does that right? Makes a choice, goes deep into it, comes back if infeasible.

@karljay7473

4 жыл бұрын

@@BackToBackSWE I haven't written any code for Sudoku puzzles, but it seems that having info on what a given cell can and can't be, helps to eliminate other paths so that you don't have to do a full check. In other words, knowing that a given cell can only be 1,2,4 you can use that knowledge to reduce the number of checks in the 3 sections (horizontal, vertical, 3x3 local grid). That should narrow down what the other one can be. I'd have to run thru your code, but seems like it's not taking advantage of complete knowledge of all paths. In other words, if you have 6 paths and you reduce that to 3 paths, you cut the amount of time needed to find the final solution. Much like the "find the hidden word" puzzle. If you see "Applz" you don't have to check it again, you know it's not a word, it can't make a word, you can mark that branch as a dead end branch using DP. I'd have to write the code to see if it's any better or doing the same thing.

Hey man, this was probably the best coding explanation, so glad I've found this video because I have the same problem waiting to be solved. The only difference is that the given board (also 9x9) is completely empty, no placement of any number whatsoever. Is there any change in the "choice" part? P.S. The code is not here anymore, any information on that? P.P.S. Keep it up, don't stop whatever you are doing!

@BackToBackSWE

4 жыл бұрын

Is there any change in the "choice" part? No P.S. The code is not here anymore, any information on that? The repository is deprecated - we only maintain backtobackswe.com. P.P.S. Keep it up, don't stop whatever you are doing! Thanks.

@newtonpermetersquared

2 жыл бұрын

@@BackToBackSWE It would be helpful if you put note about the deprecated repo in the description. But thanks for the video though 👌🏾

Good job, but where's the code?

how do you learn all these difficult algos for yourself.....

@BackToBackSWE

4 жыл бұрын

I'm a student and I just use the internets.

@amirtv106

4 жыл бұрын

Reading

Thanks for leetcode discuss 😇. Finally, found a great channel.

@BackToBackSWE

5 жыл бұрын

hahaha

I am addicted to your teaching style, I can watch your lecture whole day 😄

Awesome explanation. Backtracking makes sense now. Thank you

@BackToBackSWE

5 жыл бұрын

great

Can someone tell me where is the code I can't find it in the description

@BackToBackSWE

3 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

Where i can find the code!! Not finding in description.

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com

Hello, why filling in empty spaces is row by row ?

@BackToBackSWE

4 жыл бұрын

wym

Bro.. Please be loud Excited teacher is effective teacher. :)

yo I dont see the code in the description anyways nice video :)

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now. and thx

@aiman1562

4 жыл бұрын

@@BackToBackSWE how can i get the code if that's possible?

Why you have two 9s in ROW number 3? Is that correct?

Thank you 😊😊😊 ben

@BackToBackSWE

3 жыл бұрын

sure

In the description box above I can't find the link of your code.

@BackToBackSWE

4 жыл бұрын

The repository is deprecated and we only maintain backtobackswe.com now.

Can some one point we to the link of the code ?

Feel like a backtracking pro

I can't see the coded solution in your description😢

I was interested in hearing about backtracking part which is not there in this video.

Where is the code link? I don’t see in description

@BackToBackSWE

4 жыл бұрын

Hi, the repository is deprecated - we only maintain backtobackswe.com now

This video is much better. I like the toned down style. Good job.

@BackToBackSWE

5 жыл бұрын

I like toned down too :)

i love this man so goddamn much holy shit

@BackToBackSWE

4 жыл бұрын

no u

@sharpnova2

3 жыл бұрын

why? he left out the most important part of the algorithm and then pulled the code. he's trash.

Sorry i cant find your code could u give me the link to the code please？thank you ！

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

@sharpnova2

3 жыл бұрын

@@BackToBackSWE fuck you.

Where can I find the code?

Can u have a code for tentaizu game

@BackToBackSWE

5 жыл бұрын

yes and yes

Can you be my Algorithms professor? Lol great video! I can get my assignment done and sleep now.

@BackToBackSWE

5 жыл бұрын

I would be a professor if I had the interest but I think in this lifetime I probably won't be one.

Can u have a code for tenutio game

@BackToBackSWE

5 жыл бұрын

yes

Code in the description?

why am i watching this im still doing intro c++ lol

@BackToBackSWE

5 жыл бұрын

hahahahahahahaha no idea

@bishwhat6554

5 жыл бұрын

@@BackToBackSWE if you had to guess, what year of computing science is this?

@BackToBackSWE

5 жыл бұрын

@@bishwhat6554 I understand the intent of this question but I don't think it has an answer. It is...any year? You'd just understand this when you understand it? A 10 year old could understand this if they had proper precontext....it just happens that age brings such precontext.

Excuse me anyone please tell me where is the code

Is this solution supposed to be working for any Sudoku Grid?

@adamr-personal8035

4 жыл бұрын

Besides that - this is great channel - I am just preparing for the coding interview at Facebook, as a VR dev- and you're helping me a lot! Thanks!!!

@BackToBackSWE

4 жыл бұрын

Yes, it can easily be generalized to any Sudoku grid (forgot the exact dimensions though).

@BackToBackSWE

4 жыл бұрын

Nice, sure no problem.

Where is the link to the code?

@BackToBackSWE

4 жыл бұрын

The respository is deprecated - we only maintain backtobackswe.com

3:50 row, column traversal 4:40 we cannot break the board (dont do an n^2 check) 6:30 how do i know im finished

I love you so much

@BackToBackSWE

5 жыл бұрын

thx

inspiring ! (you compelled me to comment :)

@BackToBackSWE

4 жыл бұрын

nice

I don't think you are yelling either. Good job

@BackToBackSWE

5 жыл бұрын

aw

I can't find the codeee

where is the code??????????

@BackToBackSWE

4 жыл бұрын

depdeceted repo, no longer used

Can u please provide the code?

@BackToBackSWE

3 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

I could not find the code.please help

@BackToBackSWE

4 жыл бұрын

THe repository is deprecated but stil on my gituhb

where is the code for this problem??

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now

@prinzuchoudhury6920

4 жыл бұрын

github.com/bephrem1/backtobackswe/blob/master/Dynamic%20Programming%2C%20Recursion%2C%20%26%20Backtracking/SudokuSolver/SudokuSolver.java

um hey where is the code??

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com now.

Where is the code in the description?

@BackToBackSWE

Жыл бұрын

We maintain the code on backtobackswe.com

Where is the code?

@BackToBackSWE

4 жыл бұрын

The repository is deprecated - we only maintain backtobackswe.com

where is the code?

@BackToBackSWE

4 жыл бұрын

The repository is deprecated, it is on my github but no longer maintained

you have 2 9's in the same row :]

@BackToBackSWE

3 жыл бұрын

oops