Minimum Window Substring: Utilizing Two Pointers & Tracking Character Mappings With A Hashtable

[@BackToBackSWE]

Table of Contents: The Problem Introduction 0:00 - 1:31 Walking Through The Brute Force 1:31 - 4:19 Analyzing The Brute Force Solution 4:19 - 6:58 Lower Bounding The Brute Force 6:58 - 10:25 Let's Think Harder: Reapproaching Things 10:25 - 13:03 First Satisfying Window Found 13:03 - 13:51 We Now Make A Key Choice 13:51 - 17:43 Observing The Work The More Optimal Solution Does 17:43 - 19:25 Time Complexity 19:25 - 20:35 Space Complexity 20:35 - 21:36 Wrap Up 21:36 - 22:14 The code for both Brute Force and Optimal solutions are in the link in the description. Fully commented for teaching purposes.

[@akhilesh_singla]

Please pin this.

[@BackToBackSWE]

sure

[@akhilk5121]

The link to the code is broken.

[@mmfawzy4850]

Boss no link for the code !

[@023ankit]

@@BackToBackSWE no code in description?

[@SameerSrinivas]

Thanks a lot for choosing intuition based approach. This is the most important skill in problem solving. Thanks for your time and energy spent making these videos and for writing beautiful code. Was able to understand with no confusion. Those are very intuitive variable names! Keep rocking!!!

[@BackToBackSWE]

thanks

[@vivekgr3001]

Just love the way he explains.

[@aholagunju]

Why am I just discovering this channel? This is the best explanation I have seen so far. Makes it look simple as "abc". Thank you Ben.

[@BackToBackSWE]

haha sure

[@Egrodo1]

No request, just major kudos. Your videos are by far the best leetcode explanations I've seen, please keep it up.

[@BackToBackSWE]

I'm trying to improve daily. Teaching is hard. It is one thing to know something. But I have to sit myself down and say...how do I communicate this? The effectiveness of a teaching is inversely proportional to the number of people you lose at each great intellectual "leap" (as I always say) a concept requires.

[@neerumittal9028]

This is the most knowledge enhancing video i have seen for ds problems and it is to the point. keep the work good up.

[@BackToBackSWE]

Elated to hear that! Explore some awesome videos in our DSA course by subscribing on our website using "KZbin40" for a 40% discount - backtobackswe.com/pricing

[@doruwyl]

I've watched a lot of video explanations to different coding problems. But I can say for sure that your way of explaining things is by far the best I've seen so far. I consider that you really try your best to make the audience to understand the solution to the problem rather than just showing a problem. Well done! I hope you will keep up posting new videos! Definetively this channel should have a lot more subscribers.

[@BackToBackSWE]

yeah I will keep posting - and thanks haha, I've been at this for a while with little viewers

[@xsnowcappedx]

Man I just graduated and started job hunting. These videos have finally made everything I've studied start to come together ( I really couldn't understand a lot ). EVERY other video/explanation has been so confusing for me. You're genuinely giving me hope. Keep this up I really appreciate it. Do you plan to cover any kind of OOP design or system design/scalability questions?

[@BackToBackSWE]

Hope is the goal. And...yeah I want to do an OOP/system design thing but for that I need more independent study. I read "Clean Code" and "Clean Architecture" by Robert C. Martin. "Clean Architecture" is a fantastic, amazing, complete, book on good Object Oriented design and designing scalable OO systems. And comments like this inspire me but make me sad too. I have hundreds of more quality videos in me...will the world ever see them? ... This project will take at least a year to develop into the minimum of what I want it to be. That makes me sad. A lot of hard work and lonely days ahead in front of a computer screen...but it's ok.

[@kellyxiao3060]

@@BackToBackSWE you did really really amazing work.

[@BackToBackSWE]

@@kellyxiao3060 haha thanks

[@sahil_cse_guy2684]

@@BackToBackSWE you will be more searched on youtube in coming months if you continue to explain like this.Never ever loose hope.GOod Luck!

[@BackToBackSWE]

@@sahil_cse_guy2684 thx

[@ponderatulify]

You are a WONDERFUL educator. That's how my mind works. I can't go full abstract from the get-go. I start simple from a concrete case, specific case, then I can generalize. Always thought this was wrong, because I wasn't able to REMEMBER solutions... . Thank you man.

[@dankokozar]

Brilliant. I believe it's very hard to edit the video in a stop-motion fashion and you're making that effort. That makes your videos interesting from start to end. I also like big and clear letters (visible on tablet). Kudos!

[@BackToBackSWE]

Interesting, thanks

[@jral1127]

It took me so long to finally find a resource that makes sense. Your video and website is easy to understand and pure gold. Glad I found your channel from this problem, thanks!

[@namratam1522]

Hi Ben, I had been searching for these all problems to be explained around "Why" and "How", you have made me stop my search and I struggle to believe that someone could teach better than my expectations. I am from India and love the way you teach, amazing man.

[@BackToBackSWE]

hey -Ben

[@xiuwenzhong7375]

thanks a lot for hint of this problem. Using one HashMap to store all the target character and the times they need to show. Once the value change to 0, match length + 1, (when fast point move), once the value change from 0 to 1, match length - 1, the way to check current substring is contain target string, we can use matchLength == map.size().

[@BackToBackSWE]

I haven't replied to this for a bit, replying to close this out in my "unresponded to comments" feed.

[@jordanmoore7298]

Wonderful video. You made what could be a confusing concept into a clear one. I feel immensely more powerful behind the keyboard now!

[@BackToBackSWE]

haha nice

[@abhishekbhaware6719]

very very thank you, sir, the way you approach is just like feeding a baby right from scratch it's just awesome this problem is right now in your assignment and I don't know how to solve it but by this, I can very easily do it

[@BackToBackSWE]

nice

[@HumalDiscover]

You suddenly make the problem so easy to understand by abstracting and explaining the main thing. Thanks

[@BackToBackSWE]

sure

[@jlpeng9036]

thank you man! your explain is wonderful!!! a lot of people tried to explain their code, but you are the first one explaining how the idea (the way we should think) to solve it without coding part. i now understand it!

[@AI_For_Scientists]

teaching is an art and you are gifted with that. thank you!

[@BackToBackSWE]

Thanks! try out my 5 day free mini course for some good content backtobackswe.com/

[@TheRahul599]

I was just finding a teacher like you who teaches how to think, really you are a great teacher Sir......Lots of love and respect from India......

[@BackToBackSWE]

thanks haha, love from San Francisco

[@biswamohandwari6460]

You explain like a real man... Amazing

[@BackToBackSWE]

lol thx

[@kratigupta80]

You are doing a fantastic job I must say, and I just now saw your platform where u have put code, solution, video all at one place, and it is God level.

[@pranavganorkar2379]

One of the most readable codes - 100 times better than those on leetcode discuss - Very easy to understand for anyone - Actually had figured out the approach before watching your video - But had problems implementing it myself - Thanks Ben !

[@BackToBackSWE]

Nice, thx

[@pranavganorkar2379]

@@BackToBackSWE Just a small suggestion in your optimal code - We can maintain the frequency mapping only for required characters (those present in String t) in 'windowCharacterMapping' hashmap - As we do not care for characters which are not present in String t

[@asittripathy1778]

I am a fan of your code explanations. I must say great way to explain something in very simple way.

[@BackToBackSWE]

thx

[@kannappansuresh2447]

crystal clear explanation, thanks man. got stuck with problem for two days, I wanted a in-depth explanation of the algorithm and you provided it!

[@aasthamehtatech]

I'll mark today's date by this comment, I really did watch a few ur videos earlier, but today is when I realised the beauty of it! All this time, I jumped to problem solving directly, hoping to learn algorithm or even come up with 'em when I solve problems, now I do realise that first we need to understand the concept that deep, know y we r doing it & only then we'll able to come up with beautiful efficient soln. Also, I did like ur way of transitioning from intuitive brute force to an efficient one, that makes the content even more relatable. Thanks @BackToBackSWE :)

[@BackToBackSWE]

Thanks for the nice words -Ben

[@satyadeeproat2012]

I was confused while solving leetcode Sliding window questions. Leetcode discussion section didn't help. Watched this video and now I am able to solve most of sliding window medium level questions in 15-20mins. Thanks for the video

[@BackToBackSWE]

haha great

[@RahulVerma-fz2jf]

Really good work man. The best part is you, explaining the thinking process of how to go about optimizing brute to a better solution. Keep up the good work .

[@BackToBackSWE]

thanks and ok

[@James-yz4cc]

The clearest explanation on KZbin. You deserve way more subs!

[@BackToBackSWE]

ye

[@QVL75]

I really like the way you explained this problem. Very logical and easy to understand. Thank you!

[@kaushtubrawat8223]

I was solving some questions by myself and had doubts in some of them such as this one..and i came across your videos ..i must say you have put a lot of hard work in explanation and also in editing of your videos..hats off..SUBSCRIBED :)

[@BackToBackSWE]

thanks

[@liingpangryantee7203]

It makes so much sense when you understood the technique, but man no way would I be able to come up with this technique in an interview

[@MrAlus3]

Oh boy, oh boy. This is very good explanation. When you said this issue is consider "hard" I was suprised, since you made it so easy by breaking down this brute force and optimal solution. Cheers

[@BackToBackSWE]

haha thanks! Means a lot

[@suhasnayak4704]

Thanks! In the code while mentioning about time complexity instead of mentioning leetcode runtime, put it in terms of big o notation, that would be more helpful.

[@BackToBackSWE]

good suggestion

[@MAK28031991]

One thing which will take you forward in this domain is the way to you approach problem and optimize it further. Keep it up. All the best.

[@BackToBackSWE]

nice

[@adithyabhat4770]

I really like your approach of teaching, you start with brute force and then go on improving that. Thanks!

[@BackToBackSWE]

sure

[@atibhiagrawal6460]

I have an interview of Monday and your videos are the besttttt

[@BackToBackSWE]

nice

[@RagazzoKZ]

You are the best teacher man! Thanks!

[@BackToBackSWE]

sure

[@nikhil.pandey]

it's my 1st video on this channel............... and guess what? I love it by your approach to the solution .!!

[@BackToBackSWE]

nice

[@sophiehall38]

Expand the window until it satisfies, then contract the window. Nice explanation!

[@BackToBackSWE]

thanks. hey.

[@tushargoyal3804]

You are a brilliant teacher!!!! You really built the concepts.

[@BackToBackSWE]

thanks

[@pallav29]

Very nice explanation. Though the video is a bit lengthy compared to other videos online, but it makes concept crystal clear .

[@BackToBackSWE]

ye

[@gregoryrobertson]

Great explanation for both brute force and linear solution.

[@BackToBackSWE]

Ye

[@harishgovindan]

Well explained!! Thanks!! I would like to know how the characters are search within the window using the hash table in O(1) time.

[@BackToBackSWE]

I don't remember this problem well nor the solution enough to answer

[@tianxiaowang3771]

The Ω part is a little confused, but another part is very clear. Thanks, Ben. your video gives me a log help

[@BackToBackSWE]

Sure. And watch this: kzbin.info/www/bejne/ZqCncp-DrLmlgtE

[@darshantsdarshan1]

Somebody give this guy a medal!

[@BackToBackSWE]

ok

[@cbverma2k]

One of best explanation of complexity analysis .. keep going ... many likes

[@BackToBackSWE]

sure

[@The8merp]

Thank you for the awesome explanation of both the algorithm and it's time and space complexity. I was struggling to understand the time and space complexity.

[@BackToBackSWE]

sure

[@syedimam8663]

Your explanations are the best in the world!

[@BackToBackSWE]

thanks

[@ibrahimt09]

Very well explained!!! Thank you very much for taking the time and effort to walk through in this depth!

[@BackToBackSWE]

sure

[@Liokki]

Great explanation, thanks for the video. Helped me a lot in understanding the problem in preparation for an upcoming Facebook interview

[@BackToBackSWE]

great.

[@rohitprasad365]

Wow, This is the best explanation, Thank you for making our lives easier.

[@Yunnn_life]

Doing leetcode for 2 days and I saw you 3 times! Subscribed!

[@BackToBackSWE]

hey

[@BaishaliGhosh13]

Thank you. The example driven explanation really brings clarity to my understanding.

[@BackToBackSWE]

nice

[@edwardnewgate2198]

Amazing work dude- I'm a fan of your code explanations! Keep em coming

[@BackToBackSWE]

aw

[@jishulayek8252]

Excellent explanation!!! Really like to watch and learn from your tutorials.

[@BackToBackSWE]

sure

[@pranjalchoubey5929]

Beautifully explained!

[@BackToBackSWE]

thanks

[@ramadaskamat6418]

I wish I found this channel earlier, u r so good

[@BackToBackSWE]

welcome & no ur gud

[@tomshannon4481]

Your videos are so helpful and clear.

[@djlivestreem4039]

you're the best bro seriously never stop please

[@jakefromstatefarm3954]

absolutely brilliant! thanks for taking a chance on us!

[@laxatony]

Thanks for the clear explanation. You make the logic so easy to understand.

[@BackToBackSWE]

sure

[@youlihanshu]

so well explained, such a clear quick course!

[@vanshmittal767]

your teaching skill ismawesome man !!! love it

[@BackToBackSWE]

thanks

[@kirancoding1576]

I can only say ,"YOU ARE THE BEST"

[@BackToBackSWE]

no, I'm decent

[@Chiving]

No way someone can come with this solution on 45 minutes

[@BackToBackSWE]

Yeah

[@kanishkkumar4746]

I came to this idea just after seeing the solution and even when am not good !

[@th3tagang]

you are not being interviewed on your experience, but on your ability to memorize these problems. I know people will claim, oh, there are concepts to understand, but the reality is your ability to develop object oriented systems cannot be determined with hundreds of algorithms that have their own niche.... Unfortunately, we are perpetuating this by studying for interviews...

[@kanishkkumar4746]

@@th3tagang you are wrong buddy there are people who can solve problems without doing leetcoding (i.e. memorizing problems ) , an extreme example can be Gennady korotkevich !

[@zlmsailor]

@@kanishkkumar4746 You could not possibly find tens of thousands of them to meet the demand of FAANG.

[@xiaotongyan5394]

great explanation. I don't know how to thank you. I really like the transition from a brute force solution to an optimal one.

[@BackToBackSWE]

sure

[@Tanu-br9bp]

Just love the way you explain things. Your videos are the best. Good job 👏 👍

[@BackToBackSWE]

thanks! hey

[@Tanu-br9bp]

@@BackToBackSWE Hi, I am stuck on this question (www.lintcode.com/problem/word-pattern-ii/description). Can you please create a video for the same.

[@shashankkumarshankar3655]

You explain in such low level details with focus on the "why" than just the "how" makes you a 1000 times better than Tushar Roy's videos :P. Great work! I am pretty sure you would be great to work with in real software engineering.

[@BackToBackSWE]

thanks lol, tell that to all the companies that have rejected me 😳😳

[@southern-sunshine]

@@BackToBackSWE completely agree with shashank. BTW it's loss of companies which rejected you 😀

[@BackToBackSWE]

@@southern-sunshine ye

[@shashankkumarshankar3655]

Back To Back SWE haha. Yeah it happens. Interviews are okay with false negatives than false positives. Unfortunately that's the nature of it and nothing can be done.

[@BackToBackSWE]

@@shashankkumarshankar3655 ye

[@fridagutierrezmireles1193]

I love all of your videos, thank you for making me understand everything better!

[@BackToBackSWE]

sure

[@sciphilo754]

Lovely intuitive explanation!

[@BackToBackSWE]

Thank you!

[@Maulmota]

Excellent and clear explanation. In a sea of heavy accents and confusing explanations, you video is like water in the desert. Thanks!

[@BackToBackSWE]

thanks hahaha 🏜️💧

[@fibber7062]

Thank you for all the work you put into creating these videos! You're awesome!

[@BackToBackSWE]

nah, u are

[@ashishrawat770]

You are really a great teacher

[@BackToBackSWE]

thx

[@watcher5232]

Trust me, a very clear explanation. I will definitely donate when I pass my interview. lol

[@RDharini-yg1nm]

Very Helpful, Fantastic Explanation

[@Mohith7548]

Space complexity can be O(1) if we use array of len 26, rather than Hashtable.

[@BackToBackSWE]

ok

[@jenny3416]

there's uppercase and lowercase, and they don't treat them as the same input: s="a", t="A" output: ""

[@VijaySharma-hw4kv]

@@jenny3416 still O(1) space. if we consider all chars with 256 length

[@enigma2886]

I think I am dumb af, cOZ I hAve To KeEp rePlaYing ThE vIdEO EDIT: finally got it ! you genius teacher man !

[@BackToBackSWE]

lol great

[@nabidulalam6956]

Concise and precise explanation.

[@shashikantdivekar7839]

Very good explanation. Thank you Sir for this quality video.

[@AKHILPOKLE]

the example string looks like "adobe code banc" ,hidden message ? Thanks for explaining in a crystal clear format. cheers !

[@BackToBackSWE]

sure

[@sreerampanigrahi]

It was a very well made with emphasis on important words and points. Loved the video and you earned a sub.

[@BackToBackSWE]

welcome aboard 🚢

[@rohitpal7739]

best ! love how you cut videos

[@BackToBackSWE]

thanks

[@2k7Bertram]

Beautifully explained. Thanks!

[@BackToBackSWE]

Thank You, Glad you liked it. Do check out backtobackswe.com/platform/content and please recommend us to your family and friends :)

[@jamesdvc]

Very well explained! Saved my time and it is very helpful! Thank you!

[@BackToBackSWE]

nice

[@RuthChirinos]

I've discovered the channel, great explanation, thanks!!

[@muneerhasan]

Deserve one like from India

[@BackToBackSWE]

welcome

[@jeffenriquez9929]

Thank you! I was struggling with this.

[@BackToBackSWE]

glad it helped

[@anikpait5556]

Amazing explanation! I didnt get the part of why S was there in Space Complexity?

[@BackToBackSWE]

I don't remember this video too much

[@edin1256]

Thank you very much, this really helped a lot.

[@brandonhui1298]

was asked this by a big n, its a good problem

[@BackToBackSWE]

hey

[@brandonhui1298]

@@BackToBackSWE is for horses

[@BackToBackSWE]

@@brandonhui1298 yeah

[@Hav0c1000]

Wow... now that you explained it... I could code this with my eyes shut...

[@BackToBackSWE]

nice

[@gurpartapsingh1693]

Hey, brilliant job man. But I couldn't find the link to the code. Can you help me through it?

[@BackToBackSWE]

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

[@AngadSingh97]

Really nicely explained, thanks man!

[@BackToBackSWE]

sure

[@vekatasaiamulyapamidimukka7085]

Awesome explanation. Thank you so much for making such good videos. Helping us a lot.

[@BackToBackSWE]

sure, may the internet flourish

[@himanshu715]

Nice Explanation. Keep Going

[@BackToBackSWE]

ok.

[@gajabchudakkarbaaz2657]

superb explanation 👍 In case of brute force approach if we also consider time taken to compare each and every generated window with string t then worst case time complexity should be o(n^3) right ?

[@BackToBackSWE]

I believe so, O(n^2) windows and O(n) time to search each one

[@gajabchudakkarbaaz2657]

Ok thanks!

[@willturner3440]

Congratulations sir you got a new subscriber 🥳🥳

[@BackToBackSWE]

welcome aboard

[@pavan7959]

We know that a minimum window must start and end with the characters in string t, so we try all possible minimum windows satisfying the condition. You were trying to satisy the condition first, iam trying to minimize first.

[@BackToBackSWE]

nice

[@parvezmulla3324]

most important thing about the explanation is you taught how to come up with the solution.

[@BackToBackSWE]

yeah.

[@anonymoussloth6687]

At 14:54, when the string didn't satisfy, why couldn't we move L back to where it was and R to next position? Then the new substring would be "zjsk" which satisfies. Why do we not explore this option?

[@saharhusseini7419]

Thank you for the good explanation.