Quick Sort Using Recursion (Theory + Complexity + Code)
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- čas přidán 21. 07. 2024
- In this video, we cover the quick sort algorithm. Including the theory, code implementation using recursion, space and time complexity analysis, along with comparison with merge sort. We also see how in-built sorting algorithms work.
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=========================================
Timestamps:
00:00 Introduction
03:01 What is Pivot?
04:43 Recursive Quick Sort
09:58 How to put pivot at correct position?
17:55 How to pick the pivot?
20:15 Complexity comparison of pivot positions
27:45 Important Notes
29:32 Hybrid Sorting Algorithms
31:49 Code for Quick Sort
39:12 Internal Sorting Algorithm
41:20 Outro
#sorting #placement #dsa #interviews
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.
The confidence you have in your work, is empowering!! Keep that going
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 🤩
Such a blessing to learn DSA with your videos.😇 Please complete the series.🙂
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!
I can't even express how much value it is providing us...hats off kunal bhai!
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.
Kunal Kushwaha : "Your start is low , Your End is going to be high" :)
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,
Thanks for teaching us like no one did till now!! One small request, please make lectures on dynamic programming as well!!
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.
The way you have explained is great Kunal!
Thank You!
Kunal is very quick now 🔥
Thanks for the course ❣️
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).
you wont get 7 lakhs per month with dsa, it happens with dev
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 .
I feel very confident whenever I learn from you, Thank You for existing, God bless you!!!
thank you I actually like this implementation better than other ones I have seen. this will stick with me, no doubt
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.
thanks for uploading at this frequency.
Hope that you will cover dp really soon. 👏🙌
Wow, you are so good.
Wish you to solve complex algorithms down the lane
Hey kunal, Thanks for this course.
Best DSA COURSE on EARTH 🔥🔥
THANKU @kunal kushwaha
Thank you kunal finally understood the concept deeply.
Kunal, your tutorials are gems. I can pay for such quality content. But you choose not to. Love and Regards. Tweeting for better reach.
Bhaiya ,aap sachii mein bohot achaa padhatee hoo. Thanks bhaiya for such a course
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.
Very good explanation just loved it
good job kunal and never gave up bro keep it up
U knw bro..i think u r inborn Guru not a professional teacher.may god bless u with all Happiness of this universe.🙏
Please Use Black Background for writing on the screen
It doesn't affect eyes much 😊😊
Consider this Man
You are boosting my confidence day by day..🎉😊
Thank you so much, Kunal!
Ohh damn,
This was so well explained
45 minutes is totally worthy
Thank You!
Can anyone help me in understanding 24:50, How we got O(N^2). It is Linear Recurrence Relation, Right?
after each pass how does it ensure that pivot will end up in the correct position ?
Mad stuff ❤🔥❤🔥
Thanks a ton !!
Hey kunal please bring some leetcode sorting questions problem videos,and yes
Thank you so much for this Awesome content bro ❣️
great video bro, thank you so much!!
Great video kunal
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 😍😍😍
You're very welcome!
@@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 ?
Awesome. You make everything very easy. (In your words easy peasy 😅)
I think quick select is also a closely related technique that can be used to solve many problems.
Hey Kunal, what is the possibile time you take to complete dsa and start with Opps??
Hey Kunal , why pivot element not place correct index after one recursion call ? Although the array is sorted in the end .
Bro amazing hetric👌👌
will you make video on dynamic programming as well?
Love you kunal bhai
♥️♥️
Hi kunal, can you tell how long it will take for dynamic programming lecture??? Btw we are very thankful for your great work
Fabulous explanation..
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.
The approach which you told above does that calculate the pivot using the same mid concept?
@@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
A very informative and interesting lecture 😎
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.
@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.
I think he said , swap will not happen if it is already sorted .how? in while(s
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.
Yeah bro having same doubt
@@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
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.
@@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
@@ritviksaran6199 even this got failed @ritvik for input as {2, 5, 3, -3, -1, -22, 0, 8, 22, 9}
Great thanks for very useful content in quite comprehensive form.
I Never learnt java. Should I start this course or not?🙏🏻🙏🏻
Yes
Love u kunal bhaiya❤❤
best videos here!
god level explain ❤️
Awesooooooooooooome ❤️❤️
Thank you Kunal
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..
Hey , pls tell me one thing that how the primary condition is working , that break condition , that if(low>=hi) return ;
best course till date in any platform
Hey Kunal, How did you do the DSA at your time? Like did you rely on tutorial videos or some book?
@kunal Please continue this course...
Thanks Kunal
Best explanation
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
If I use any other element as pivot instead of middle element, it gives stack overflow error. Can someone help me through this issue?(same algorithm)
Hey bhaiya,
How to stay away from -ve people? and stay focused toward own goal(SDE OR DATA SCIENTIST).
Thank you sir
Hi Kunal, are you planning to launch any playlist?
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.
brother i am not able to solve the linear recurrence relation because the function is f(n) = f(n - 1) + O(n) . When I put a^n for f(n) what to put in place for O(n). I am confuse in that part can anyone help me to understand ?
This is by far the simplest explaination of Quick Sort that i have found
Thanks a lot man
How to find the index of the pivot element by using this algorithm ?
loved it..
@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
why did you delete your old videos?? where do we find them now?
pls upload dp series soon
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.
Can someone suggest can we take mid ele as pivot
Great teaching please make a video on heap sort as well...
Sure I will
AMAZING
hey can you make a video about how to apply remote jobs ...
My profssor seriously needs to learn from this dude, I was stressing about this so much, this titorial is elite. THANK YOU SO MUCH
Fabulous
still watching consistently
😀😀
😀😀
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 ?
Kunal i am waiting for some other topic vedio please kindly upload it
I am going to have my placement in next sem
Can anyone help me in understanding 24:50, How we got O(N^2). It is Linear Recurrence Relation, Right?
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
Nope
Check out the Time and complexity video, You'll get a whole great idea
Do a separate series for Dynamic programming bro..
Can you please continue this course and complete it soon
13:14 pivot at correct position❌every element at correct position✅
Hey kunal bring some leetcode maximum subarray type questions problem videos
I will
ku ku ku kunal...kunal....kunal.....kunal.....
Would u pls make a tutorial on regex
My java code is not compiling at 38:21 any solution ?
Just wow
this quick sort algorithm not given correct ans for (5,4,1,2,8,7,6,3) can you explain it why?
use variable int pivot = arr[mid] not just compare with arr[mid] directly
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
it works well for 2,4,5,3. it gives 2,3,4,5
@@rishavraj6861 yeah, I noticed that but it works like that only when we are using the high = n instead of n - 1.
@@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.
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
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.