Quick Sort Using Recursion (Theory + Complexity + Code)

[@KunalKushwaha]

DSA + interview preparation playlist: kzbin.info/aero/PL9gnSGHSqcnr_DxHsP7AW9ftq0AtAyYqJ

[@mokka_comedy]

Hi kunal, u are the best, could you pls complete entire topics on DSA

[@hc-dc7043]

One of the best explanations I've seen for Quick Sort. The way he broke the concept down to its nuts and bolts is really amazing.

[@Tomharry910]

I remember plucking out my hair on recursion and sorting algos before stumbling on your videos. You explain it very well and its very intellectually satisfying to watch your videos as well.

[@nishantsingh8477]

There's this merge sort and quick sort, people say its hard to understand this and so I left them and proceeded further in my DS journey. But I was damn sure you will make it easy and so listened to you and Now I know this . Thankyou KK Bhaiya 🤩

[@Sillysmiles76]

Such a blessing to learn DSA with your videos.😇 Please complete the series.🙂

[@zainabfahim8714]

The confidence you have in your work, is empowering!! Keep that going

[@sagarmore9425]

I have tried to understand merge sort and quick sort literally a thousand times. In college, classes, some time by me. I was not able to visualize how it is actually working with recursion, although I knew the code. But the way, you are simplifying the things and the way you have had the first recursion video done is just awesome. That first recursion video is quite important and on top of this you explained this sorting so well, kudos man!

[@AshishKumar-ys7rj]

best lecture on yt for quick sort because it is the most efficient i have seen, but first watch the quick sort algorithm by striver, he will clear all the doubts if you have got any by watching this lecture , since i had lot of doubts . Once you understand the algorithm u can follow the code here . The concept will be crystal clear then .

[@vidhijain2945]

The way you have explained is great Kunal!

[@KunalKushwaha]

Thank You!

[@rohitchilhorkar8114]

I can't even express how much value it is providing us...hats off kunal bhai!

[@mk_ahmar]

Hey Kunal, your lectures are valuably explained, and covers everything one should know sooner or later. For example after watching this QuickSort lecture, all I've to do is practice some question, I don't need to watch any more concept of this anywhere, and this is amazing. You and your video lectures are underrated, if this quality of lectures are provided by any EdTech they would have charged that course extravagant. Hope I'll be able to get ₹7Lakh/month 😂(Joking).

[@KunalKushwaha]

you wont get 7 lakhs per month with dsa, it happens with dev

[@shantahiremath7313]

Thank you Kunal Sir. You are always the best teacher. I never learned this sort by fearing the complexity. But now you made it a cakewalk. Always grateful.

[@karthikpm9669]

this is good...i mean its good that you didnt advertise your videos in a humble way , because people wont know how good your videos are. PS i didnt realise how fast time went , the way you taught was very smooth and seemed like a story to me.

[@VinodKumar-fn2iq]

Kunal is very quick now 🔥 Thanks for the course ❣️

[@tejasvijain1077]

Before watching this vid, i was on gfg and javapoint understanding what quick sort was and my god, kunal has explined it so well and he hasnt copied what they did and I was blown by how easy he has made this!! Kudos bro,

[@shikhamaurya4453]

Ohh damn, This was so well explained 45 minutes is totally worthy

[@KunalKushwaha]

Thank You!

[@twi4458]

Can anyone help me in understanding 24:50, How we got O(N^2). It is Linear Recurrence Relation, Right?

[@ritviksaran6199]

after each pass how does it ensure that pivot will end up in the correct position ?

[@sravansunkara]

I feel very confident whenever I learn from you, Thank You for existing, God bless you!!!

[@SochtaHoonMain]

Kunal Kushwaha : "Your start is low , Your End is going to be high" :)

[@rakeshkumarmaurya8265]

Best DSA COURSE on EARTH 🔥🔥 THANKU @kunal kushwaha

[@Mohit_Gupta24]

As always brilliant explanation. I used to be scared of quick sort in my college days, but this video makes it seem really easy. Moreover, I was able to relate Step: placing pivot at the correct index with Binary Search step. In binary search, we search for a target element, assuming the array is sorted, and use the start and end indexes as pointers to the virtual array. Here we have to just place the pivot at the correct index, so instead of searching the target, we already have the target(i.e. pivot), we have to put at correct index and in this process we are ensuring elements less than pivot are on LHS, and elements greater than pivot are RHS.

[@santoshkumarpandey8372]

Amazing, if You dont understand first time, please re-re listen. it is amazing

[@Helly_Patel]

Thanks for teaching us like no one did till now!! One small request, please make lectures on dynamic programming as well!!

[@VishalKumar-pk9ek]

In the merge sort video , I was little confused in the concepts of sorting algorithm through recursion but by this video , the previous confusion also got cleared . Thank you so much 😍😍😍

[@KunalKushwaha]

You're very welcome!

[@vikassk1308]

@@KunalKushwaha little confused, when you say pivot would be in the correct position after swaps if I have below array and I choose 4 as pivot {8,6,1,4,2,12} after swaps, ill end up having {2,4,1,6,8,12} where 4 is at index 1 but it should be at index 2 right ?

[@jyotiprakashnayak1123]

best course till date in any platform

[@shivamrana4633]

You are boosting my confidence day by day..🎉😊

[@nishu0766]

i request you to please upload all the remaining topics of this complete DSA bootcamp as soon as possible

[@Cloud-577]

thank you I actually like this implementation better than other ones I have seen. this will stick with me, no doubt

[@devanshgaur1747]

Bhaiya ,aap sachii mein bohot achaa padhatee hoo. Thanks bhaiya for such a course

[@charaiveticharaiveti8414]

Kunal, your tutorials are gems. I can pay for such quality content. But you choose not to. Love and Regards. Tweeting for better reach.

[@vinaykrishna747]

Please Use Black Background for writing on the screen It doesn't affect eyes much 😊😊 Consider this Man

[@piyush9266]

U knw bro..i think u r inborn Guru not a professional teacher.may god bless u with all Happiness of this universe.🙏

[@anshulgoel1940]

An alternative approach is to swap the pivot with the last index before we start in each recursive call and then start comparing left and right. Once index cross over, we swap pivot with left pointer. Works out much cleaner at code level.

[@pratheeeeeesh4839]

The approach which you told above does that calculate the pivot using the same mid concept?

[@anshulgoel1940]

@@pratheeeeeesh4839 No. Pivot can be picked in any way. It won't make any difference at complexity level. This approach I suggested just keeps the code clean. Hope it helps

[@requisits]

Thank you kunal finally understood the concept deeply.

[@anjalithakur_12]

Very good explanation just loved it

[@KshitizAnand-xr1wj]

I really loved this sorting algorithm

[@Content_creater_entertainment]

Best vedio❤

[@sravanakirtana2787]

Awesome. You make everything very easy. (In your words easy peasy 😅)

[@civuasdev5532]

Hey kunal, Thanks for this course.

[@harshaggarwal1821]

@36:05 you mentioned swapping doesn't happen if array already sorted. But taking {1,2,3,4,5} it does call swap with same indices.

[@chennayaianjc3306]

I think he said , swap will not happen if it is already sorted .how? in while(s

[@gitansh194]

00:05 Quicksort is a crucial sorting algorithm frequently asked in interviews. 02:11 Quick sort uses pivot to divide elements into smaller and larger groups. 06:22 Quick Sort uses recursion to position the pivot element correctly after each pass. 08:20 Quick sort uses recursion to sort arrays efficiently 12:24 Understanding how to identify violations while sorting using Quick Sort. 14:35 Moving the pivot to the correct position using recursion 18:43 Picking the pivot element in quick sort 20:34 Understanding time complexity and recurrence relation in Quick Sort. 24:23 Quick sort's time complexity is O(n^2), covered in detail 26:22 Recurrence relation of merge sort explained with time complexity formulas. 29:36 Hybrid sorting algorithms combine merge sort and insertion sort for efficiency. 31:26 Exploring new approaches to solve problems is recommended. 34:59 Moving elements according to pivot and violating conditions 36:36 Explanation of the swapping process and recursion call in Quick Sort using recursion. 40:23 Quick sort is a hybrid sorting algorithm 41:58 Quick Sort using recursion is a common sorting algorithm.

[@suyashkumar8840]

Love you kunal bhai ♥️♥️

[@924_aradhyapatro5]

This is by far the simplest explaination of Quick Sort that i have found

[@baap6382]

Wow, you are so good. Wish you to solve complex algorithms down the lane

[@amruthaa5876]

Thank you so much, Kunal!

[@geetankarkarmakar378]

Mad stuff ❤‍🔥❤‍🔥 Thanks a ton !!

[@KartiKKaushiKYt]

My profssor seriously needs to learn from this dude, I was stressing about this so much, this titorial is elite. THANK YOU SO MUCH

[@poojakatare1497]

A very informative and interesting lecture 😎

[@ritviksaran6199]

Kunal bro this is a doubt. After a pass of the outer while loop, how can we confirm that pivot will end in correct index? For the array {1, 4, 2, 5, 7, 6, 3} after one pass changes to {1, 4, 2, 3, 7, 6, 5}. 5 was the chosen pivot but it does not end in correct position. The whole algorithm is correct at the end it will give the sorted array, but for this version I think we cannot confirm that after each pass pivot will end up in correct index.

[@harcharansingh1997]

Yeah bro having same doubt

[@ritviksaran6199]

@@harcharansingh1997 This method ensures that in each pass the pivot ends up in the correct index public class Main { public static void main(String[] args) { int [] arr = {1, 4, 2, 5, 7, 6, 3}; quickSort(arr, 0, arr.length - 1); for(int i : arr){ System.out.println(i); } }public static void quickSort(int [] arr, int low, int high){ if(low >= high) return; int s = low; int e = high - 1; int pivot = arr[high]; while(s pivot){ e--; } if(s

[@MohamedElsayed-pb3oj]

The reason you are having doubt is because the algorithm is incorrect. Tried it manually and tried it with the debugger and it still gave the first pass answer. Meaning the algorithm doesn't put the pivot in its intended location.

[@takenbysac]

@@MohamedElsayed-pb3oj exactly Elsayed , this algo is wrong, I tried with negative numbers as input and it failed . Tried with {2,5,3,0,8,22,9,-1,-3,-5} as input . @Kunal

[@takenbysac]

@@ritviksaran6199 even this got failed @ritvik for input as {2, 5, 3, -3, -1, -22, 0, 8, 22, 9}

[@akashpradhan7908]

I have tried some udemy courses, watched some KZbin tutorials on DSA ... But damn.. Kunal is a teacher of another league.

[@talish7714]

good job kunal and never gave up bro keep it up

[@ashishgaikwad440]

god level explain ❤️

[@NavanshK]

@kunal Please continue this course...

[@Dekh_rha_hai_vinod.]

Bro amazing hetric👌👌

[@randheerkumargautam6433]

will you make video on dynamic programming as well?

[@abhirajchatterjee6965]

This partitioning algorithm seems to be incorrect, say we take the same example provided in the video wherein the last element is always selected as the pivot - 10, 80, 30, 90, 40, 50, 70 | p = 70, s is at 10, e is at 70 now, s moves till 80 where it finds a violation (element at s should be less than 70, here it is > 70), e stays at 70 since it is also a violation(element at e should be greater than 70, here it is = 70 ), swapping happens -> array after first swap -> 10, 70, 30, 90, 40, 50, 80 -> s moves to 30, e moves to 50 notice that the new part of the array which is going to be partitioned now is 30,90,40,50 and the rest is assumed to have been placed correctly w.r.t the pivot that is 70, which is wrong as 70 is clearly not at the position where it is supposed to be.

[@siddharthgowd825]

you were wrong, dont partition array after single swap, go unil i

[@absingh773]

13:14 pivot at correct position❌every element at correct position✅

[@vikaspanwar5194]

thanks for uploading at this frequency. Hope that you will cover dp really soon. 👏🙌

[@ImranicShow]

Kunal, you are a great teacher. I didn't comment in all other videos because those were flawless to understand. This one was fantastic till you started implementing the algorithm. You explanation of the core algo, complexity analysis etc were awesome. However, you said, after every pass all smaller element should be left side of the pivot and all larger element should be in the right side of pivot. But in your implementation this is not the case. I mean after you swap, it just swap two elements, doesn't gurantee the position of pivot we want after the first pass. But I was wondering how your implementation still works. I traced this implementation in pen and paper and found why it's still working. It's a bit unorthodox implementation of quick sort. This doesn't work without any modification, if I change the pivot from mid to first or last. Anyway, I found solution in internet where they make the partition based on the pivot. Those solutions works whatever(first, last or mid) I made pivot. Overall, to me it seems this implementation may confuses the new commers. Anyway, your explanation of the algo is out of question, clarify a lot of confusions. Being a software engineer for more than half a decade, I recently decided to brush up my DSA and you are helping me a lot. Keep up the great work.

[@smilemania5102]

Awesooooooooooooome ❤️❤️

[@akashnagar4862]

Before starting this course, i was like ''Java is very tough language'', but after dig into this course till now, I am like ''Java is Fun'', Thankyou man for providing such great course. And I would like to request you that please make a course of Collection framework also. And you will be boom on KZbin....trust me the way you transfer your thoughts is really amazing. Cheers to the hard work 🥂

[@kirankumar9729]

Fabulous explanation..

[@charon71]

best videos here!

[@NilavraPathak]

I think quick select is also a closely related technique that can be used to solve many problems.

[@mrrishiraj88]

Great thanks for very useful content in quite comprehensive form.

[@prikshit_sharma4071]

I Never learnt java. Should I start this course or not?🙏🏻🙏🏻

[@KunalKushwaha]

Yes

[@yourmentor8242]

Hey kunal please bring some leetcode sorting questions problem videos,and yes Thank you so much for this Awesome content bro ❣️

[@akshaykumar-wd8jc]

Great video kunal

[@karanbadhwar4113]

The problem is I did not understand the Time and space Complexity After recurrence relation, as I am do not understand the Maths that you did, it took me more than a week to any how complete the video, but now my question is how can I do that, as I did not understand them Maths you taught, any other way to solve it ?

[@jk-sm6qr]

Thank you Kunal

[@MuhammadAnas-t1z]

For those who were asking that the algorithm will work fine but after first pass the pivot element is not at the correct place. Here is the update version of the code public static void quickSort(int arr[],int low,int high){ if(low >= high){ return; } int s = low; int e = high; int mid = s + (e-s)/2; int pivot = arr[mid]; while(s pivot){ --e; } if(s

[@vanshsharma2486]

great video bro, thank you so much!!

[@kishorevb8331]

With the code you provided, it will not place the pivot at the right spot after one pass, but still it works!!! It doesn't place the pivot in the right index due you incrementing and decrementing the start and end after each swap. We must increment and decrement only when provided that the value in that index is lower than or higher than the pivot

[@abhisheknigam6975]

Thanks for this series Kunal, just have one question that how would we do this with return the result, as at the 2 last lines of the code we are again calling the function so to write return statement there

[@ayushmaheshwari809]

Hey Kunal , why pivot element not place correct index after one recursion call ? Although the array is sorted in the end .

[@firdoshansari2757]

Hey Kunal, what is the possibile time you take to complete dsa and start with Opps??

[@sourabhkothari7014]

Best explanation

[@anukritisingh4479]

pls upload dp series soon

[@imTiwari2005]

bhaiya what about dp and greedy

[@prashantmishra9220]

@kunalKushwaha Bhaiya aapne to book follow krke pdhai ki hogi....to hmlog sirf is playlist ko follow krenge kya sach me utna hi knowledge gain kr paenge...kya is playlist me jitna pdhaya gya hai utna hi pdhne se sach me acchi job crack kr paenge? pls reply

[@twi4458]

Can anyone help me in understanding 24:50, How we got O(N^2). It is Linear Recurrence Relation, Right?

[@Rahul-nw5rp]

Yes man . For this you have to use substitute method . I checked common algorithms book and there was written that to use akra bazee method bi must be in range of 0 to 1 exclusive

[@Sumit-lr1qj]

Nope

[@vcrohithutagonna2105]

Check out the Time and complexity video, You'll get a whole great idea

[@arpitanaik4940]

​@@vcrohithutagonna2105 Still not able to get it. Can you plz share how to got the ans.

[@parmarkamlesh6493]

Hi Kunal, are you planning to launch any playlist?

[@ViGyaTam]

Thanks Kunal

[@frosted_soul_]

ku ku ku kunal...kunal....kunal.....kunal.....

[@dinbandhusharma4568]

thanks for this amazing knowledge I really like your video 🤗🙏🏻

[@joshiomkar1394]

Hey bro, I followed your implementation of quicksort, and the array is sorting fine, but there is a problem. Suppose there is an array [2, 4, 5, 3]. Here pivot will be the middle element at index 1 which is 4. Now, all the elements less than 4 should be on the left of 4 and greater at the right, but using your implementation. The resulting array becomes [2, 3, 5, 4]. 4 will get swapped with 3 because 4 and 3 breaks the violation. Then, start will increment and end will decrement and both point to 5. start will break the violation while end doesn't and keeps moving back until 3. Here further swapping will not take place because start > end. To note that the array becomes sorted in the next step because recursion calls quickSort on [2, 3] and [5, 4] but why didn't the 4 get placed in the right position. Is this a behaviour of quicksort or am I missing something? Please respond because this is really confusing me

[@rishavraj6861]

it works well for 2,4,5,3. it gives 2,3,4,5

[@joshiomkar1394]

@@rishavraj6861 yeah, I noticed that but it works like that only when we are using the high = n instead of n - 1.

[@rishavraj6861]

@@joshiomkar1394 how will u take high = n. n is the size of array so, for last index high = n-1. in this video high is also equals to n-1.

[@nikhilsood6126]

you are right brother......after first pass .....acc. to his theory the left of pivot must be less than pivot but it is not after first pass.......in implementation.......so it was also confusing me.......in actual acc. to his implementation only right will follow the theory not left

[@ritviksaran6199]

True, Actually you said that on the second loop, [2, 3] and [5, 4] will be passed, that is not true, [2, 3, 5] and [4] will be passed. This technique works but it does not ensure that pivot will end up in the correct index. I think he was wrong in that point.

[@shyamalm88]

Kunal Facing too much problem with sliding window technique. with strings and other things, it will be very helpful if you can create a video on this with solving some problems, not only the maximum sum problems but other problems also some tips or tricks will be fine. Love your work. your content really helpful.

[@bishalbhattacharjee850]

Great teaching please make a video on heap sort as well...

[@KunalKushwaha]

Sure I will

[@programmer6953]

At 23:07 i dont get why we put pivot at middle while showing t(n) calculation ,at t=0 the left will be empty but right will be n-1 element does it mean we picked first element as pivot ?if not why we showing pivot in t(n) calculation why not just t k +t n-k + alfa n supposedly pivot is at the end of the array for better presentation pls enlighten me on this..

[@PiyushMishra-tq6cl]

Hey Kunal, How did you do the DSA at your time? Like did you rely on tutorial videos or some book?

[@rudram4534]

still watching consistently 😀😀 😀😀

[@mohammedsaad0761]

The video explains the quicksort algorithm in detail, covering its theory, complexity, and coding implementation, while comparing it with other sorting algorithms like merge sort and discussing internal sorting functions in Java and Python. Detailed Summary for [Quick Sort Using Recursion (Theory + Complexity + Code)](kzbin.info/www/bejne/kGnWp4KnltKUnZo) by [Monica](monica.im) [00:04](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=4) Understanding the importance of Quicksort in sorting algorithms - Introduction to Quicksort and its significance in interviews} - Covering the complexity, time, space, code, advantages, and disadvantages of Quicksort} - Exploring internal sorting algorithms and hybrid sorting techniques} [05:15](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=315.199) Explanation of quick sort using recursion - Explanation of partitioning elements based on a pivot} - Role of recursion in sorting process} - Unique aspect of pivot placement in quick sort} - Recursion's role in sorting the left and right partitions} - Selection of a new pivot element for further partitioning} [10:33](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=633.44) Explanation of how to perform quick sort using recursion - Explanation of selecting the pivot element} - Identifying violations in the elements compared to the pivot} - Fixing violations by swapping elements} - Comparison and handling of elements in relation to the pivot} [15:49](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=949.04) Explanation of the quick sort algorithm using recursion - Explanation of choosing the pivot and dividing the array} - Demonstration of the pivot at the correct position} - Discussion on picking the pivot element} - Introduction to complexity analysis} - Partitioning the elements based on the chosen pivot} [21:07](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=1267.12) Understanding the time complexity of Quick Sort using recursion - Explaining the time taken to put the pivot at the correct position} - Discussing the recurrence relation of Quick Sort} - Analyzing the worst-case scenario in Quick Sort} - Illustrating the impact of choosing the smallest or largest pivot element} - Highlighting the consequences of the worst-case scenario in Quick Sort} [26:22](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=1582.48) Explanation of time complexity and space complexity in Quick Sort - Detailed explanation of time complexity using Akra-Bazzi formula} - Importance of understanding space and time complexity in algorithms} - Best case and worst case complexity of Quick Sort} - Stability of algorithms and the concept of stable sorting} - Previous video covering sorting algorithms and stability in detail} [31:40](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=1900.48) Introduction to Quick Sort Using Recursion - Starting the coding part for quick sort} - Explaining the concept of low and high indices} - Using pointers to manipulate the object in the array} [36:57](kzbin.info/www/bejne/kGnWp4KnltKUnZo&t=2217.68) Explanation of quick sort using recursion and its implementation - Explanation of the recursion process in quick sort} - Dividing the array into two halves for sorting} - Initialization of low and high variables for sorting} - Discussion on different approaches to quick sort} - Recommendation to try other sorting methods before asking for help}

[@MainakBhowmick-vw3sh]

13:05 oops i think i made a mistake ,, and that look

[@mihirjadhav5642]

why did you delete your old videos?? where do we find them now?

[@abhijitmanna4524]

My java code is not compiling at 38:21 any solution ?

[@RaviPatel-rj1re]

this quick sort algorithm not given correct ans for (5,4,1,2,8,7,6,3) can you explain it why?

[@amine_fadssi]

use variable int pivot = arr[mid] not just compare with arr[mid] directly

[@LifeWithGunjann]

Can you please continue this course and complete it soon

[@itsom5294]

Hey kunal bring some leetcode maximum subarray type questions problem videos

[@KunalKushwaha]

I will

[@sangamsaini138]

bhaiya if conditon lagana ka koi jarurat nahi tha uska binna bhi ho jata becouse loop me bhi same conddition hai or isliya if condition likhna ki koi jarurat nahi thi

[@Videolyy]

loved it..

[@nihal.n6329]

pivot won't fall in the correct index after the first pass

[@AdarshKumar-xh1ie]

Hi kunal. I tried this array int[] arr1 = {1,9,2,3,5,6,7,8,10} on the above code. In the end the array was sorted. But, after the first pass the 5 was on the 1st index before 2 and 3 after taking 5 as the pivot. So is there any other way around for this? Or its working fine?