Quick Sort For Beginners | Strivers A2Z DSA Course

[@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

[@nimishjais9666]

Same

[@ictfan-ly8gh]

Not same 😢

[@deepanshuthakur140]

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

[@navagharkiran5769]

then you haven't tried Abdul Bari

[@deepanshuthakur140]

@@navagharkiran5769 sadly I did, its not that abdul bari is not good, its me who is dumb uk but striver made me understand it anyhow

[@parshuramry1657]

@@navagharkiran5769 abdul bari is better for college academics but striver is for campus selections

[@Kaushik846]

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

[@kingreja5894]

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

[@PunjabPrank]

yes i am thinking about this mistake ..thank you

[@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.

[@dreamer12n]

Hey can you give me the code for pivot = median element pls??

[@onlyone7209]

​@@dreamer12nwhat kind of code do you want

[@itsmehere8285]

​@@dreamer12nJust set pivot = (low + high)/ 2 or in a better way to deal with larger numbers make it low +(high -low)/2

[@ParasSharma-mf8or]

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

[@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❤

[@FunkyPanda6263]

1 video every 2 days... Seems TRUE ❣️

[@parthmangalkar]

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

[@isaacreyes7563]

Damn, I have been looking at sort, recursion, etc forever. I was first confronted with merge/quicksort back in 2019. Been looking at them from various other sources over the years but nobody ever explained it like you do. You are absolutely amazing at this stuff. Idk where you are in life but I hope you go onto make amazing things because someone with this in depth knowledge shouldn't be stuck teaching!

[@tanmayjivnani865]

Don't worry he is working at Google. Doing great in life :)

[@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

[@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

[@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.

[@pranshuatrey]

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

[@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 🙂

[@ArunKumar-sk9jl]

A great man with the best of the best teaching skills and a kind attitude to make it free is awesome ❤

[@keshariaman]

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

[@ShivamGupta-xw6gh]

best explanation of quick sort on youtube

[@makerNg1817]

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

[@mityamkumar1158]

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

[@darkelixir2517]

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

[@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

[@shubhamagarwal1434]

#Free Education For All...... # Bhishma Pitamah of DSA...You could have earned in lacs by putting it as paid couses on udamey or any other elaerning portals, but you decided to make it free...it requires a greate sacrifice and a feeling of giving back to community, there might be very few peope in world who does this...."विद्या का दान ही सर्वोत्तम दान होता है" Hats Off to you man, Salute from 10+ yrs exp guy from BLR, India.......

[@gurudev8543]

Best explanation ever ❤️❤️❤️ Thanks bhaiya

[@rayyanrahim7413]

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

[@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

[@nirmaljyotibiswas752]

shouldn't it be while(i > j) ?

[@CodeBoost8375]

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

[@rajkumarvb5197]

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

[@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

[@madhumithaakula7666]

Thank You anna because of u I have learned something new today🙂

[@Manoj_IIC-Admin]

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

[@Jaishreeram-ly2jm]

Yes bro.👊 😊

[@adityamukherjee2207]

bro you are a true saviour !!

[@tusharkhandave374]

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

[@shubhamsahu492]

Your explanations are the best 💕👌👌

[@abdulwahabshaik1686]

Understanding everything u r teaching to us u r magician striver

[@AniketSingh-gm9nh]

u r just amazing. keep educating man u r blessing for us.❤

[@onetapgaming123-v2x]

16 Aug 2024, 2:00 a.m.🎯🔥

[@pradeep6635]

understood Bhayya.The best explanation in youtube😎

[@subhadeepghosh2813]

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

[@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 ?

[@OmPrakash-268]

awesom explanation , love it learning DSA .

[@SharathS-s9i]

for the assigment problem just change the condition while (i < j) { while (arr[i] > pivot && i

[@yashlakade179]

Thanks Striver :)

[@CycoTrend]

bro is the angel!

[@hemantyadav6198]

Awesome explaintion ❤

[@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

[@prithukathet193]

tusi great ho tofa Kabul karo.

[@scoc55vora15]

Best , Detailed and Crisp

[@shivamcanada]

very well explained brother appreciate your efforts

[@rishabhkumar-qs3jb]

Excellent explanation :)

[@bonammadankumar681]

You rocks the DSA

[@rohanraj2604]

Crystal clear bhaiya 😍

[@Malayalam_learner]

Why not ilow Can anyone explain why striver doesn't take these ??

[@sakshamtyagi2969]

Completely Understood 👍👍

[@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 !

[@hareshnayak7302]

Understood,Thanks striver for this amazing video.

[@manavsingh5919]

Understood sir.....u r the best👍💞

[@yhbarve]

Understood bhaiya! Thank you

[@meshkatuddinahammed]

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

[@tamoghnasaha2667]

Why we are using while (i

[@anuragpawar4497]

Step-2 completed! Understood

[@Pawankumar-i8c]

thank you so muchbhiaya for this masterpiece

[@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?

[@Kirito045]

Understood Striver on TOP!

[@Gcoder18]

nice way of explaination

[@student_03]

checking for out of bounds like this makes it simple and natural while (i pivot) { j--; }

[@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.

[@cinime]

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

[@THE-MYSTIC]

Thanks striver this video helped me ❤

[@makingthamilan1592]

you are my God , thanks man 🥰

[@Hipfire786]

understood everything sir so far all sorting techniques

[@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 + " "); } } }

[@poojaraman6663]

Understood...thank u sir🙂

[@samarthpai5359]

Understood sir. For descending order: int partitionFunction(int arr[], int low, int high){ int i = low, j = high, temp; int pivot = arr[low]; while(ipivot and i

[@user-kk4qv5fy6k]

Why can't we give while (i

[@The_Shubham_Soni]

Best Teacher

[@lwnflash2123]

Is recursive stack space not required while computing space somplexity?

[@saranshgautam3011]

Why do we ignore recursion stack space when calculating Space Complexity? I think that should count.

[@soumelee5661]

Awesome explanation! TYSM for the videos

[@yashpandey7]

understood , Step 2 completed :)

[@Gurunat16]

26:58 That will be |1 3 2| 4. Right?

[@ankit-yj7hk]

understand bhaiya !!! thank uh so much

[@harshalparanjiya5850]

let's go --> 20 december 🔥🔥

[@ankiitttkmmm]

man you awesome Thanks

[@joydeepdas29]

Understood 😄. But will you please explain why we swapped between (arr[j] , arr[low]) instead of (arr[j], pivot)?

[@takeUforward]

I will recommend you to take examples and do a dry run, that will help you immensely to learn! I can answer, but finding out yourself on pen and paper is what will help you grow :)

[@joydeepdas29]

@@takeUforward Thank you. I will surely do as suggested 😄.

[@elizabethr5161]

We have taken low as a pivot, so it doesn't matter whether we swap it with low or pivot.

[@Anonymous-ej2xo]

@@elizabethr5161 No it will matter because you want the swapping to occur between the elements of the array. With what you are saying, the j-th position will get the correct value, but 'low' position will not have been swapped. The swapping needs to occur in the array. You are getting confused as the values being swapped are effectively the same, but where the swap occurs is not the same.

[@prajjwalkohli9830]

pivot is just some another independent variable having same value as arr[low], swapping with pivot means swapping values with an independent variable, we want swapping with the array's low itself so we explicitly use arr[low] here.

[@raynwani137]

Love you bhai!

[@____Akash__]

After long time ❤️❤️

[@krishnakanttiwari517]

Thank You So Much Sir

[@ByteBuilder-b6u]

Should be include stack space in recursion problems while stating space complexity ?

[@AbdullahKhan-et6qo]

Was eagerly waiting for your videos 🙌

[@arnavanant3049]

you are OP bhaiya

[@_hulk748]

Thank you sir🙇‍♂️🙏❤

[@JothiprakashThangaraj]

Understood!! Thanks!!!

[@dayashankarlakhotia4943]

Good explanation us

[@shreyashkumarsahu5985]

understood Thanks a lot sir

[@DeepakKumar-xj4ul]

for decreasing Quick Sort:- 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 quickSort(vector &arr, int low, int high) { if (low < high) { int pIndex = partition(arr, low, high); quickSort(arr, low, pIndex - 1); quickSort(arr, pIndex + 1, high); } } vector sortArray(vector &arr) { quickSort(arr, 0, arr.size() - 1); return arr; }

[@techniciangurugaming5020]

UNDERSTOOS VERY WELL

[@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

[@adityabedi266]

22-01-2025 completed this topic learn a lot about quick sort. Thanks sir 😊 //code in java package Sorting; import java.util.Arrays; public class QuickSort { public static void main(String[] args) { int[] arr= {8, 3, 9, 2, 5, 6, 4, 1}; quickSort(arr, 0, arr.length-1); System.out.println(Arrays.toString(arr)); } static void quickSort(int[] arr, int low, int high){ if(low

[@basusingg4882]

Very well understood!

[@sugarfreecode]

Quick Sort in Descending Order (C++): int partitionArray(int input[], int start, int end) { int pivot = input[start]; int i = start; int j = end; while (i < j) { while (input[i] >= pivot && i < end) { i++; } while (input[j] < pivot && j > start) { j--; } if (i < j) { int temp = input[i]; input[i] = input[j]; input[j] = temp; } } input[start] = input[j]; input[j] = pivot; return j; } void quickSort(int input[], int start, int end) { if (start >= end) return; int partition = partitionArray(input, start, end); quickSort(input, start, partition - 1); quickSort(input, partition + 1, end); }