Quick sort in 4 minutes
ฝัง
- เผยแพร่เมื่อ 24 มิ.ย. 2024
- Step by step instructions showing how to run quick sort.
Code: github.com/msambol/dsa/blob/m... (different than video, I added this retroactively)
Sources:
1. Data Structures and Abstractions with Java by Frank M. Carrano [www.amazon.com/Structures-Abs...]
2. www.algorithmist.com/index.php...
LinkedIn: / michael-sambol
![[Watch Party] APL 2024 Bacon Time Vs Hong Kong Attitude ชนะเข้ารอบ](http://i.ytimg.com/vi/ikUfW81sDaw/mqdefault.jpg)
This is great video! but, I feel the algo provided in the end is not the same as the way he was explaining.. I went ahead and wrote my code for it same way he explained:
```
class Solution:
def sortArray(self, nums: List[int]) -> List[int]:
def quicksort(nums, lo, hi):
if lo < hi:
partition_resting_point = partition(nums, lo, hi)
quicksort(nums, lo, partition_resting_point - 1)
quicksort(nums, partition_resting_point + 1, hi)
def partition(nums, lo, hi):
pivotIdx = random.randint(lo, hi)
nums[pivotIdx], nums[hi] = nums[hi], nums[pivotIdx]
pivot = nums[hi]
l_idx = lo
r_idx = hi-1
while l_idx
Yeah, in the early days I didn't spend enough time on pseudocode. Trying to fix that now by building out this repo: github.com/msambol/youtube/blob/master/sort/quick_sort.py. Thanks for the feedback!
@@MichaelSambol I got really confused when the pseudocode didn't match the explanation. You should correct that (in the video) ASAP.
@@westsideslasha I'm sorry about that! TH-cam won't let me change the video now unfortunately, but I pinned this comment.
I am encountering an infinite loop if I change the while condition to be i < j instead of
i am glad that i looked at the comment section after having a hard time connecting the pesudo code to the video content.
With every new quick sort video, I watch, I get more recursively confused.
same lol all the quicksort videos use the same words to explain it
hey man, after pulling my hair out for 2 days I finally got it, sadly I had to pay for it.
@@user-wp9pz9hl3z what did u pay for?
@@HACKINGMADEFUN a Udemy course
@@user-wp9pz9hl3z cool
Guy: "I think you understand the concept"
Me: No I don't
it gets halved and is recursively applied to both halves in each step
@@Evokans um what?
@@sleevman2307 It gets repeatedly done on each new half, as after each half the pivot is in the right place, so a new pivot is used.
@@faith2756 sorry wat?
@@sleevman2307 Which part exactly do you not understand?
I feel so dumb when i don't understand this, but then i just scroll the comment section and realise that im not alone lol
understanding the meaning of pivot is the KEY.
yeah, theitemfromleft, or right wasn't even properly discussed, left of what or right of what exactly?
lol
i should be working at mcdonalds
You really should. *SAD!*
@@SkillUpMobileGaming You too
wait what. why
lol 😂😂😂
that's what I was thinking. you're a genius pal
So we let magic handle the rest.
HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA
After you swap itemFromLeft and the pivot at the end, itemFromLeft is now at the end of the array. So, use that as the *new* pivot.
Repeat that until its sorted.
@@airex12 so 8 is the new pivot? How can I go through if there is no number in the array greater than 8?
@@kennethquilantang8080 after 7 is put in its correct position, remember that all numbers to the right of 7 are greater than 7. In this case, there is only one number - 8. A partition with just one number is already sorted, so you can ignore it and move on to sort [6,5] to the left of 7.
For sorting [6,5] choose 5 as the pivot. itemFromLeft is therefore 6, and itemFromRight has no value because no number in the array smaller than 5. Therefore, we can stop and swap itemFromLeft and the pivot to leave [5,6].
Yes, the video is unclear because it does not explain these cases. The point is that each time you put the pivot into it's correct position, you have "split" the array into two parts - one part has all numbers bigger than the pivot and the other part has all numbers smaller than the pivot. Parts with *just one* element are already sorted. If a part is already sorted, no itemFromLeft can be found. If a part is unsorted, you are guaranteed to find an itemFromLeft, and if the index of itemFromRight < the index of itemFromLeft *OR* itemFromRight does not exist then you can swap itemFromLeft and the pivot to put the pivot into its correct position in the whole array.
@@airex12 I get your point bro thanks but what would be the next step. Will I need to pick another pivot? How can I sort the rest?
*screams in Ross voice* PIVOT! PIVOT! PIVOT!
haha, I can't help imaging Ross's face, hahaha
Me in future, oh Ross's couch sort?
screams in Chandler voice SHUT UP! SHUT UP! SHUT UP!
Oh my GOOOOD :-))))))))))))) So truuuuueeeeeee
This is exactly what came into my mind learning about this :))
To ones without enough background knowledge, this video omits details of execution of each step. But to ones with, this is concise and covers sufficient key points of quick sort. Thanks a lot for your video sharing.
Thats the fanciest wording I've heard, i would use: "You get it or you dont"
Try to sort a few short sequences yourself according to the steps in the video. You may get the "background knowledge".
i put this at 1.5x and now i learnt quick sort 2.6667 minutes
The psudocode is not intuitively reflecting the walkthrough
I've been looking at it for a few minutes now, and I can believe that this pseudocode is accurate, but I'd have to check the details of what the partition function is doing to be sure, but it seems legit. Assuming your language of choice will permit a self-referential function like that.
@@diabl2master The recursion is fine... he's talking about how `partition` is putting the pivot on the left wall instead of the right. In the video the pivot is on the right side.
@@jscholex That would be a failure of technically reflecting, not intuitively reflecting, the walkthrough. I'm not sure OP was referring to that, but who knows.
@@diabl2master Yeah who knows... but I think we can all agree the pseudocode isn't great hah
the pseudocode shows the Lomuto version but the visualisation is for the Hoare version, which is better. See Wikipedia for both.
How to get Confused in 4 minutes
then again, this was the best video about it so far
I want more videos like this where they explain stuff in less than 10 minutes
Bet ? th-cam.com/video/Zh37XyQLHkw/w-d-xo.html
there's a video by abdul. i think it is best
am still confused
N Betancourt cuz the way he explains it IS confusing
I’ve watched this a couple of times, thought I understood went to the exam and screwed up
Now that I’ve watched other videos I understand that the way he explains it is confusing
N Betancourt He made it more confusing, for sure.
He didn't explain what quick sort does in general, what it can be applied to, and left some holes in the explanation that someone with no experience would struggle to grasp. Which is a shame.
Hope this helps :th-cam.com/video/Zh37XyQLHkw/w-d-xo.html
i hope you got it cute bird from nichijou
you should put the code next to all of the visual aids and highlight each line as its being done in the visual. thanks for the help with sorting!
when i search for something on youtube and see one of your videos in the results i genuenly get excited
That is the exact! same Quick Sort Algorithm we have been thought. Really good! Thanks
Yess I finally understood it, having a clear mind the morning before the exam helped
This is great. The simple explanation and the especially simple pseudocode towards the end makes it easy to understand the core concept of the algorithm.
I watched several videos, including my school books, and I had no idea what they were saying with left to right and could not get the answers in the correct order because of that. I was able to understand after watching your video and it allowed me to get past my assignment. Thank you.
Your short videos helped me a looot. Thank you so much!
I study computer science, and once, I had an exam with a few sort algorithms in it. I didn't really study but about twenty minutes before the exam I watched your 2-4 minute videos on these sort algorithms and I passed the exam. Thank you for helping me.
thats gonna b me td lmao
@@fireboywatergirl1625 i am sure you are at the right place.
These are some clean tutorials. Thank you for making this!
I think I'm here for the fourth time now.
These 4 minute videos are great for cramming!
Wow... You just found a place in my mind where you stored quick sort so deeply.🙋💖😂
Imagine newcomers watching this explanation for the first time.
Thank you. I feel the same about my actual online course I'm studying. And I'm a newcomer. I feel better.
horrible
very well explained and visualised!! thank you!
If anyone is confused at the 1:10, basically he doesn't go through the loop.
Instead he jumps to when item from left is higher or item from right is smaller etc. There is a left and right pointer that checks for the condition and then left++ or right-- if its not correct.
itemsfromRight goes from 1 cuz its smaller, and then the right-- checks 7, not smaller, right--, checks 8 not smaller, right-- and then it checks the 0 and see that its smaller.
Thanks for the explanation!
what the hell are you talking about this is a church sir
@@jamboy1843 I don't even remember making this comment.
watching this video from NEPAL.
Great sir. THANK YOU.
It was quick and I understood everything. Thanks a lot
This is the first video that made me really understand how to impl quicksort, and it's very short.
This is exactly what I was looking for in a video
Nice! Glad to see magic still exists!
This is the most confusing and incoherent visualization of quicksort I've ever seen
Well said 👍
Makes perfect sense to me
Christian May That’s so great! 🙌👏
I thought the visualisation was fine. I feel that I understand it now.
This is the fist visualisation of quick-sort I've ever seen, so I know it doesn't mean much, but I agree.
LOL this is one of the best and easiest video out there on quick sort. All of you disliking it shouldn't do programming.
Thanks for the concise and succinct tutorial.
I have a question: if I skip using a "while" the smaller elements from the beginning than pivot is not more efficient? And I think that because the computer is exempt from doing the first swaps
I guess, In the quicksort explanation he moves the pivot to the RIGHT END of the array.
In the pseudocode, he moves the pivot to the LEFT end of the array. And after the swapping is done, he then brings the pivot to the original position from the LEFTEND.
I've seen too many quicksort algorithm videos and this works the best for all my cases.
it's 8:48 AM, i have an exam at 15:30 PM and ur saving me here
Psuedo code does not match demonstrated algorithm.
The pseudocode is hard to read, but the variable name "leftwall" is really good, this gives me a vivid concept of how the leftmost larger item was swapped and the "wall" moved.
pseudocode is actually wrong as well !
@@hiteshsahu_ Exactly, not only 1 pointer moves & stopping when this 1 pointer reaches end of the array, but also only picking leftmost value as pivot
@@hiteshsahu_ Exactly , i have wasted so much time over it
@@blurryhorizon I suppose that in the Partition function, the "pivot = A[low]" should actually be "pivot = A[high]"? Very confusing so I wrote it down and found out that the pseudocode doesn't work properly. // Oh just realised that although pivot = A[low] might works as well but the pseudocode is totally wrong for Partition function jeez..
@@scarlettwang2146 I think it should be as it is. Something else is wrong.
Helped me. Great vid. Fan of your since now. Cheers.
currently studying for my Algorithms and Data Structure exam, your video is very helpful :)
thanks
Thank you so much, i have a pc science test today, and i didn'T understand since i can't speak german that well and i am still learning it, this guy explained it all
This was exactly the kind of video I was looking for!! Short and concise, but no loss of information. Thank you.
Thanks Brother, You save my 10 min exam fast revision time
You did a great job man! It helps me a lot . Thank you so much.
Perfect explanation of quick sort!!
this made it a lot more logical for me, thank you.
Thank you so much! I was having so much trouble understanding this algorithm but you saved me in 4 minutes.
people are complaining but this is gonna come in clutch for my wirtten exam tmr.
This is a good explanation, thanks !
I actually understand a little bit now, thanks!
Thank u very much Sir, I got it completely. Actually I'd missed my college online lecture b/c of sleeping... U saved me just night before exam, as urs is the shortest video on YT.
The video hold the key of quicksort, most clear to me!
Great videos I like your work :) It is very easy and quick .. All the best for future videos and work
I'm seeing myself working customer service for the rest of my life
Thanks, it really helped.
Thank you for the video. I am grateful for your time and contribution. Kind regards, Akira.
That without voice over made the video from great to perfect
this is a very clear explanation, thanks
QuickSort has always been a bit of a mystery to me, but somehow this video instantly made it click. Thank you so much!
thank u so much, i have an exam tommorow and was stressing bc i couldnt figure out how quick sort work with my teacher's explanation and this just simplified it easily. tysm ;-;
explained it much fckin better in 4 minutes with 1.5x watchspeed than my teacher in a 90 minutes class, thank you sm
Thank you so much! Just understood how to do a quick sort in a few minutes. Fantastic Video! Keep up the great work 😀
Thank you finally understood quicksort
😌😌
The visualization is perfect!
Michael Sambol, You're amazing! Let's be friends and have fun together!
This algo is akin to a toddler randomly sorting numbers around until they're in order
I was able to write quick sort in a day when I first learned it, and now I completely forgot and feel stupid. This is my major, how tf did I forget this algorithm.
solid video mate
amazing, ive got an exam tmrw... this lesson is much appriciated as my professor is not very good at explaining these basics
Excellent explanation
The comments on this video do not reflect the like/dislike ratio.
here for the comments
VERY UNIQUE TASTE 8|
Wtf
Great explanation, thancc lots!
Thank you. Vell explained. and easy to understand
Great tutorial! Actually I understood this concept from this video in less than 4 mins.
Brilliant video mate!
Thanks. Great video
I am glad I read the comment to know that I am not the only one!
I feel like the pseudo code would reflect the presentation a lot more if we let pivot be A[high] with rightwall=high-1. Then the conditional statement to initiate swap would be if(A[i]>pivot), and of course having rightwall=rightwall+1
makes sense to me. Thanks!
brilliant explanation
This guy is amazing.
all your videos are short and very useful.
THAnk you very much..
Hey, Thanks for the explanasion, It was a clear and concise video, however the pseudocode is somewhat wrong I believe in 3 things:
In Partition, the order of operations is not correct: increment leftwall first, then swap.
The final swap in Partition is not correctly swapping the pivot's original position with A[leftwall].
The recursive calls in Quicksort should be updated to exclude the pivot_location from the ranges, properly dividing the array into segments that exclude the sorted pivot.
here is the corrected version:
Quicksort(A as array, low as int, high as int)
if (low < high)
pivot_location = Partition(A, low, high)
Quicksort(A, low, pivot_location - 1)
Quicksort(A, pivot_location + 1, high)
Partition(A as array, low as int, high as int)
pivot = A[low]
leftwall = low
for i = low + 1 to high
if (A[i] < pivot) then
leftwall = leftwall + 1
swap(A[i], A[leftwall])
swap(A[low], A[leftwall])
return(leftwall)
Thanks again!
Him: “quick sort = pivot”
Me: “WHILE HE HID IN RADIO WE PIVOTED TO VIDEO 🗣️💥”
Thanks for clear explanation. Correct Position for Pivot, let recursive do remains. Good job man.
How do you find the median of three "middle" value on an even number of elements in a list?
Hvala ti brate pomogao si mi puno u životu
saying "move pivot" but instead swapping it with last number 🗿👍🏻
0:10 who else thought of Ross screaming Pivot from that Friends Episode
that was quick, indeed
i cannot even describe how much i hate learning these, thanks for the video it helps a lot
How do you pick the item from left, based on what? I know it has to be larger but in the video you chose 6, wouldn’t 5 also work?
bro thanks for this kick-ass video
Thank you dude you save me from the finals.....
thank you
dont know if people will still answer questions on this video, but i tried implenting this, but i have a problem with when there's two or more copies of the smallest value it gets stuck because it tries ti continue until the index of item from right is at the end of the list, but since there are multiple of the same values at the end of the list, index of item from right doesnt continue to decrease.
Basically: how do i check that it has completed one pass and the smallest/largest item is at the end?
FINALY SOMEONE WITH CLEAR INSTRUCTIONS