Quick Sort For Beginners | Strivers A2Z DSA Course

Notes:
Problem Link: bit.ly/41sTzt8
Full Course: bit.ly/tufA2ZYt
Notes/C++/Java/Python Codes: takeuforward.org/data-structu...
You can follow me across social media, all my handles are below:
Linkedin/Instagram/Telegram: linktr.ee/takeUforward
0:00 - intro
1:10 - Flow Chart
3:28 - Explanation of the Algo
19:29 - Psuedo Code & Dry run
27:32 - Note about comparator signs
29:01 - Important Point
29:52 - Online code
32:31 - Time Complexity and Space complexity
34:22 - Outro

[@takeUforward]

Let's march ahead, and create an unmatchable DSA course! ❤ The worst case complexity will be O(N ^ 2) if we end up choosing the largest or smallest element as the pivot always. We will add this in the notes in the description. I missed this in the video.

[@yashhokte1020]

Yes striver , even i was thinking same that you didn't explain this thing , btw thankyou so much for this much crystal clear explaination ..

[@anookimmidisetty2939]

Hi striver @takeUforward , when are you going to release video solutions for string type problems and heaps?

[@yaswanthmitta8983]

There is a minor mistake in your algo at 23:54 in while loop condition must be arr[i]

[@teen_python_go9947]

Since, we are always choosing pivot to be the first element of the array, we can always avoid the O(n^2) case by pre-checking if the array is pre-sorted (with O(n) Time Complexity) and if it is not then only feed it into the quick sort function.

[@yashsharma6112]

I have to state it that "I tried to learn all sorting techniques various time. I learned but after a few days I forgot. But when you just added the real meaning of each sorting techniques. Like why it is called as selection sort and so on.... SO now I just remember their meanings and write the algorithm on my own." Thank you very much. Loved your teaching style

[@vedantgolash6084]

same here

[@anusha6033]

same heree

[@chiranjeebpanda8926]

same here

[@deepanshuthakur140]

I tried to learn this from every yt channel but striver is the one i got it from, respect++

[@adityamaheshwari4250]

Really you make everything a cakewalk! Thank you so much sir, it takes a big heart to do such a lot for the community for free❤

[@ParasSharma-mf8or]

Thanks for this amazing lecture,this is my humble request please complete this course as soon as possible.

[@parthmangalkar]

Understood! Thank you!! You are the best! Thanks a lot for making this DSA playlist! It really is helping me a lot!

[@FunkyPanda6263]

1 video every 2 days... Seems TRUE ❣️

[@Kaushik846]

Probably one of the crisp and to the point explanation of quick sort algorithm available online!!

[@keshariaman]

Thanks a lot for Quick Short. Feels easier to understand 🥰

[@ashokasamrat8375]

Thanks for recursive effort brother.And till now all your lectures are absolutely awesome 🔥🔥

[@meshkatuddinahammed]

Can't thank you more. Great lectures. Appreciate it.

[@cinime]

Understood! Super amazing explanation as always, thank you very much!!

[@pranshuatrey]

This is gold... Plz keep doing this..

[@AdityaSharma-hs8os]

please upload full course you are douing a good job bhaiyaaa ,you are really a honest teacher other youtubers who has million subscribers just make us fool on name of dsa course ,they just tell the problem and paste the soultion but you solve every aspect -f our doubt please cpmplete this and dont worry of views and watch time,time will come when everyone will know who is the best teacher on youtube for dsa

[@active_akasa8429]

striver you are the best out of best....this tutorial is just amazing and you are like god for us A big thank you so much for your effort 🙂

[@makerNg1817]

it's very understandable way you teach. thank you for this amazing lecture

[@rajkumarvb5197]

Manhhhh 🥵, you are awesome. I can see the effort you are putting in! Thanks a lot! ❤

[@mityamkumar1158]

Understood.... 💯💯 Excited for Arrays playlist❤

[@ShivamGupta-xw6gh]

best explanation of quick sort on youtube

[@soumelee5661]

Awesome explanation! TYSM for the videos

[@animeshmishra6280]

how do you know which doubts are going to come in my mind. GREAT LECTURE SIR 🔥

[@edisane8763]

Because once he was also in the same place as we are now and he worked hard to reach this point now he is helping us

[@ahssanakhtar5746]

Excellent content about DSA .I am follwing you A-Z coarse and improve my self in DSA day by DSA Thanks for making such a amazing content

[@abdulwahabshaik1686]

Understanding everything u r teaching to us u r magician striver

[@tusharkhandave374]

Thanks for giving this content for free it helps me a lot

[@SwatiSingh-ys6hm]

Damn it, i have learnt sorting algorithms a lot of times, but i aways manage to somehow forget.But after seeing this video now i understand it in so much more detail and depth which i earlier didn't even notice. thanks you soo much striver !

[@scoc55vora15]

Best , Detailed and Crisp

[@gurudev8543]

Best explanation ever ❤️❤️❤️ Thanks bhaiya

[@darkelixir2517]

Understood, will be a quick way to remember the algorithm, well taught!! Thanks

[@omkarsawant9267]

Quick Sort's in-place partitioning makes it more memory-efficient than Merge Sort in practice, but the worst-case space complexity can be higher when the partitioning is unbalanced. Time Complexity: Best Case: O(n log n) when the pivot choices consistently lead to balanced partitions. Average Case: O(n log n) Worst Case: O(n^2) when the pivot choices consistently lead to unbalanced partitions. However, with good pivot selection strategies (e.g., using the median element), this can be mitigated. Space Complexity: O(log n) auxiliary space for the recursive call stack in the best and average cases. O(n) in the worst case when the partitioning is highly unbalanced. Quick Sort's in-place partitioning makes it more memory-efficient than Merge Sort in practice, but the worst-case space complexity can be higher when the partitioning is unbalanced. Quick Sort tends to perform well in practice and is often faster than other O(n log n) algorithms, but its worst-case time complexity is worse than Merge Sort. Merge Sort's space complexity makes it less memory-efficient compared to some other sorting algorithms, but its stable performance and guaranteed O(n log n) time complexity in all cases make it a preferred choice for certain scenarios. Space Complexity: O(n) additional space is required for the temporary arrays during the merging process. It has a space complexity of O(n) due to the need for additional space for merging.

[@Jinntechive]

Appreciate the effort you put for writing this comment 😇❤

[@nayankhuman1043]

Thanks for the comment. i was looking for it.

[@lakshmitirupatamma2139]

Thank you so much sir for this content. Very good explanation

[@tanmaykarmakar6224]

Quick sort in Descending order-(PYTHON) arr=[25,1,8,7,32,2,5] def piviot(arr,high,low): piviot=arr[high] i=high j=low while(i=piviot and i

[@sumitapathak2900]

Hey I haven't done a dryrun of your code but as i has index of high how can in increment in the while loop?

[@jayaveersai1446]

yes make sense and have to chnage the while (i

[@alessandrocamilleri1239]

Excellent explanation as usual. Thank you. I am posting the iterative version which should further save on recursion call stack space. I have used a queue as the data structure but stack works just as well. void quickSort (vector &nums) { int n = nums.size(); queue q; q.push({0, n-1}); int low, high, pivot, i, j; while(!q.empty()) { low = q.front().first; high = q.front().second; q.pop(); if (low >= high) continue; pivot = nums[low]; i = low; j = high; while (j > i) { while (nums[i] pivot && j > 0) j--; if (j >= i) swap(nums[i], nums[j]); } swap (nums[low], nums[j]); q.push({low, j-1}); q.push({j+1, high}); } }

[@balakrishnanr648]

So Yah u tried the iterative version of Quick Sort but still you are using the space what the Recursive func calls use in func call stack in the QUEUE FORM. O(logN) Queue takes as extra space. Like the point is Quick sort no matter what -> You can further optimize. Func Stk Space or in Iterative normal stack or queue space is needed. As we need to store it somewhere -> what are the next range of places where it is unsorted. Either use the system's func call stack or make ur own.

[@hareshnayak7302]

Understood,Thanks striver for this amazing video.

[@AbdullahKhan-et6qo]

Was eagerly waiting for your videos 🙌

[@pradeep6635]

understood Bhayya.The best explanation in youtube😎

[@revathiP9185]

Thank you bhaiya. Amazing explanation ❤

[@THE-MYSTIC]

Thanks striver this video helped me ❤

[@sumit49]

us!! please add it in the same playlist as that will be more organised . ❣❣

[@DevashishJose]

Understood. Thank you so much.

[@manavsingh5919]

Understood sir.....u r the best👍💞

[@rohanraj2604]

Crystal clear bhaiya 😍

[@rishabhkumar-qs3jb]

Excellent explanation :)

[@Hipfire786]

understood everything sir so far all sorting techniques

[@Manishgupta200]

Here is my Assignment question solution : #include using namespace std; int partition(vector &arr, int low, int high){ int pivot = arr[low]; int i = low; int j = high; while(i < j){ while(arr[i] >= pivot && i = low + 1) j--; if(i < j) swap(arr[i], arr[j]); } swap(arr[low], arr[j]); return j; } void qs(vector& arr, int low, int high){ if(low < high){ int pIndex = partition(arr, low, high); qs(arr, low, pIndex - 1); qs(arr, pIndex + 1, high); } } int main(void){ // vector v = {4, 3, 2, 1}; vector v = {4, 3, 2, 1, 4, 7, 5, 6}; int n = v.size(); qs(v, 0, n-1); for(auto it : v) cout

[@waibeeYB]

Understood bhaiya! Thank you

[@gulammohammadali4831]

Very well understood 🙂

[@basusingg4882]

Very well understood!

[@subhadeepghosh2813]

Kaha se sikha hai aise padana? vai koi vi nahi hai tumhare jaisa. Maza aa gaya

[@rayyanrahim7413]

love from pakistan we need these type of legend to teach progamming

[@bonammadankumar681]

You rocks the DSA

[@mansiyelgulwar4765]

Understood Thank You!!!

[@Manoj_IIC-Admin]

at time 23:52 it should be pivot not ar[pivot] thanks bhaiya

[@ankit-yj7hk]

understand bhaiya !!! thank uh so much

[@ankiitttkmmm]

man you awesome Thanks

[@sakshamtyagi2969]

Completely Understood 👍👍

[@yashpandey7]

understood , Step 2 completed :)

[@bhagyashreekhairnar683]

Thank you thank you !!

[@NazeerBashaShaik]

Understood, thank you.

[@harshitjaiswal9439]

Amazing!

[@kingreja5894]

//for descending while (arr[i]>=pivot && i

[@_hulk748]

Thank you sir🙇‍♂️🙏❤

[@konankikeerthi]

Thanks bro.. understood

[@dayashankarlakhotia4943]

Good explanation us

[@____Akash__]

After long time ❤️❤️

[@diyaarora3199]

Wonderful Explanation!! Notes include the space complexity as O(1)+O(N) auxiliary stack space. Is it the worst case space complexity? And is the best and average case auxiliary space complexity O(logN)?

[@The_Shubham_Soni]

Best Teacher

[@user-ut2te7td7e]

After checking all lectures on internet...None has explained better than you

[@preetisahani5054]

Its a great video, but you should also explain the cases where complexity for quick sort can result to O(n^2) in the case where all elements of array are same and when array is already sorted, in those cases partition will always be 1, n-1.

[@krishnendughosh2368]

sorted or even if sorted in descending order complexity will be n^2

[@manish_mnnit]

For Descennding Order Sorting -> //Just Reverse the inequality sign in partition function :- #include int partition(vector&arr,int low,int high){ int pivot =arr[low]; int i=low ,j=high; while(i

[@nayankhuman1043]

Understood ! ❤

[@makingthamilan1592]

you are my God , thanks man 🥰

[@jassbawa955]

UNDERSTOOD!

[@tasneemayham974]

CODE FOR DESCENDING (JAVA): public void quickSort(int[] arr, int low, int high){ if(low low){ j--; } if(i

[@DineshKumar-pw7qb]

When I try to run this code(using array), I getting no output and the code runs for infinite time. When I try with ArrayList, I am getting output. Explain why? This put me into severe headache

[@tasneemayham974]

@@DineshKumar-pw7qb Heyy!! You mean my code? Either way, can you send me the code you are working on. I want to try it. How about that? Maybe we can fix it together?

[@DineshKumar-pw7qb]

@@tasneemayham974bro are sure about your code is working well with array?

[@tasneemayham974]

@@DineshKumar-pw7qb Hey, mate! I copied my code, and yes it works with arrays. It doesn't give me errors or infinite loops, but... this line: while(arr[i] > pivot && i < high) I missed the =. I am so sorry. I should be: while(arr[i] >= pivot && i < high) Check it out now. But as I understand, the problem with your code is the array itself, yes? Not the output? If you want you can send the code. Because mine works well with array. P.S.: I will edit the original comment, and put the equal.

[@ankush8243]

Thank you bhaiya!

[@nagame859]

Understood 👍

[@zyzzbrah9429]

int partition (int arr[], int low, int high) { int p=arr[low]; int i=low,j=high; while(i=p && i

[@shailesh3348]

I also completed 2 steps can we connect?

[@juhichoudhary9281]

Understood ❤️‍🔥

[@khalasianiket816]

understood ❤

[@her_soulmate]

Understood 🎉

[@arnavanant3049]

you are OP bhaiya

[@Kirito045]

Understood Striver on TOP!

[@eshaanpandey7353]

Thanks

[@YourCodeVerse]

Understood✅🔥🔥

[@lwnflash2123]

Is recursive stack space not required while computing space somplexity?

[@AbhishekKumar-cd4gg]

// for descending order just we have to do the tweaks in the how we are selecting elements when which we are stopping when we are finding element smaller in left and stop when we find the element greater the pivot then we just we swap it than it goes in the recursion stack public class Quicksort { static int partiton(int arr [] , int low , int high ){ int pivot = arr[low]; int i= low; int j = high; while (i < j ) { while (arr[i] >= pivot && i = low + 1 ) { j--; } if(i < j ){ int temp = arr[i]; arr[i] = arr [j]; arr[j] = temp; } } int temp = arr[j]; arr[j] = arr[low]; arr[low] = temp; return j ; } static void quicksort(int arr [] , int low , int high){ if(low < high ){ int PartionIndex = partiton(arr,low,high) ; quicksort(arr, low , PartionIndex-1); quicksort(arr, PartionIndex+1 , high); } } public static void main(String[] args) { int arr [] = {10, 80, 30, 90, 40}; int n = arr.length-1; quicksort(arr, 0, n); for (int i : arr) { System.out.print(i + " "); } } }

[@ayushsagar9183]

understood🔥

[@johndurai2226]

understood striver bro

[@sangeetha_1403]

Understood🙏

[@venugopal_2003]

understood!

[@ranjanworld5450]

I will watch the next video now

[@user-tk2vg5jt3l]

Thank you Bhaiya

[@KartikeyTT]

tysm sir

[@abhimanyusingh4906]

UNDERSTOOD

[@naveensaicremsiyadlapalli3769]

Super

[@shaiksoofi3741]

Thank yyou

[@sid17_cgdyt]

// condition i

[@user-uv5or5bm2c]

Understood!!

[@deepak8720]

Understood. :)

[@sonalikharwar4269]

Instead of 3,2,1 it should be 1,3,2 coz we have done swapping b/w 4 & 1 like swap(arr[low], arr[j]) right ?

[@nikhild.20]

Understood!