Quicksort Sort Algorithm in Java - Full Tutorial With Source

Full tutorial for the Quicksort algorithm in Java, with source!
Quicksort is widely considered the best sorting algorithm out there, but it can be very complicated to learn.
We'll walk through the entire quick sort sorting algorithm step by step, then walk through coding the entire thing in Java.
Quicksort doesn't have to be so tough to learn!
Learn quicksort by watching the whole algorithm being described and coded.
Learn or improve your Java by watching it being coded live!
Hi, I'm John! I'm a Lead Java Software Engineer and I've been in the programming industry for more than a decade. I love sharing what I've learned over the years in a way that's understandable for all levels of Java learners.
Let me know what else you'd like to see!
Source here: www.codepile.net/pile/X6lXog6G
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[@CodingWithJohn]

A few viewers have pointed out an issue where a value would be out of order in some situations. A couple of commenters, Wilson Barbosa and Yebo Qin, identified what the issue was and implemented fixes and noted them in comments below. I've included Wilson's fix in the linked code, so now it should all be working properly. Let me know if anyone notices anything else though. Thanks so much to everyone who saw this and proposed fixes! This community is clearly awesome. Also, this is why code reviews are a great idea!

[@wbarbosabr]

You're welcome, John! And keep up the good work!

[@yeboqin5892]

no probs, you ve done a great job !

[@TuanBuianonymous]

@@yeboqin5892 which case is it? please give me example

[@duytuannguyen8323]

​@@TuanBuianonymous 15:49, line 43. There's an edge case. It's not absolutely the pivot will smaller than the left pointer.

[@goldfish-bloopbloop]

@@duytuannguyen8323 thank you so much!

[@ginom219]

Prepping for a coding interview in Java and I’ve gotta say, your videos are the best and easiest to follow that I’ve come across. Keep up the good work

[@captainjacksparrow1328]

Hey, how was interview? I hope you got a job

[@vladimirgorlin7510]

It worths to mention that quicksort algoritm has in avarage O(nlog (n)) time complexity

[@MrDarshD]

Well explained with the array visualization and the actual code creation process. Highly appreciate your time and efforts, John! Thank you so much!

[@luanakimley2367]

Thank you for these videos, they're the clearest I've found so far! Hope you keep making more 😄👍

[@emekaukwuoma9507]

Thank you John, you have just taught me quick sort algorithm in a way that is clear and understandable. I enjoyed watching and learning from your videos.

[@morhakak1907]

Hi John, Your explanation was crystal clear + the last tweaks - the best quick sort tutorial on youtube right now.

[@mindofpaul9543]

Dude, You are so good at explaining these things! Thank you for making these more complicated parts of coding easier to understand for a novice like me!

[@Dalcenn]

Seeing you explain this with the visuals made this so much more understandable than watching my professor do it on a chalkboard! Thank you for this explanation and the sample code. Another great video John.

[@shwimwhearz4819]

Instant sub, no one breaks down theses concepts quite like you John. Glad a found this channel

[@YerushalayimShelZahv]

Big thank you for sharing and teaching. I wish you much success with your channel and hope you continue producing more content. I look forward to your videos!

[@jeffreyslominsky7656]

Your teaching is brilliant John, thank you for sharing!

[@IsaacCode95]

great stuff! i really like your videos and the way you explain stuff!, i still had to rewatch this a second time to understand the code behind it, thank you!

[@namrathas5804]

Thank you so much John, your videos are really a blessing to us. Its so easy to understand bcz of the visualization you make while explaining. thanks for your effort.

[@muhammadmuaaz3704]

The explaination using the numbers was amazing bro I literally understoop every single word.

[@ralfiasz]

Definitely the best there is. Talking about your content obviously. You’ve helped me so much I couldn’t possibly thank you enough Sir!

[@siomarapantarotto]

Thanks so much, John! I loved the way you explained QuickSort. 😍

[@codewithbug]

thank you, man. this is my fourth quick sort video and none of them are doing coding part. thank you, really.

[@lindascoon4652]

WOW, you have the talent of teacher. Thank you for making these videos.

[@yavuzaydn6410]

The explanation was amazing. Thank you John

[@mockingbird3809]

This is honestly the best explanation on entire KZbin!

[@Garrison86]

Awesome explanation! really appreciate the time taken to make these videos.

[@jugalsingh5176]

Thank you for making us learn Java clearly and understand deeply😊

[@narendrakumariitb]

Thank you so much John💚. What a great teacher you are 👏

[@kannanbalasubramani5541]

I wasn't this clear of quick sort before watching this one.. It helped a lot. thank you!

[@DarkLightning96]

Great video, one of the best explanations of quicksort I've come across! It could've been better if at the end you compared quicksort with other sorting algorithms just to see the difference in the time it takes to sort arrays as they grow larger. Maybe you could do that in another video :)

[@MTB_Bay_Area]

Thank you, it is helpful that you show how it is done on a text file and you are moving the numbers in the text boxes. it is good visualization of the process.

[@Joshua-te1fg]

This tutorials tips like over loading and eclipse method maker gave me so much joy

[@RK-zg9cd]

Thank you very much, John! I tried to find out working quicksort algorythm for Java, but the only one I found out has big bug. But thanks to you I won't be dropped out of my university))

[@mabeleain3320]

Thank you so much John. Best explanation I've ever seen.

[@ikennanana]

Thank you so much for this video! You've really helped me get a grapsp on the QuickSort algorithm other than my professors over here...

[@wiilwaal258]

I dont know how i can thank u.. It took me yrs and never understood quicksort .. With ur tutorials i understood everything clearly. Thanks man 🥰

[@sibrimbarcenasreales5525]

You are a really good master, thanks i think this could took me weeks to understand it well, but you made it so easy !

[@user-ci5gj9ks8o]

You're literally the best, thank you! Eagerly looking forward for new videos from you🤓

[@jaecheokkim99]

Very easy and clear explaination! Thank you so much.

[@AndrewLapteff]

BEST tutor about quicksort in universe!!!

[@millerlou7294]

This video will only 30k+ views explains the concept clearer than all other more popular videos, this guys deserves more subs!

[@fredericoamigo]

Thank you so much for this (and all of your other vids). You truly have an extraordinary ability to explain difficult things in an understandable and nicely communicated way. I simply love your vids! Keep up the good work!

[@CodingWithJohn]

Thanks for the very kind words!

[@abdurrouf4159]

Damn. Your presentation is too smart. I really fall in love on your teaching approch. I knew how the quicksort works. But, couldn't able to make understand others properly how this sorting algorithm works. You demostrated these things nicely.

[@adeyinkaolurin]

Thank you John. Your explanation is very understandable...

[@nehemie_n]

Clear and understandable way! Smooth and smart!

[@RAWRIHATEYOU1]

thank you so much John! I was getting really frustrated with myself because I've watched 3 quicksort tutorials, and the last video the comments were like "if you dont get it, you dont get it." felt really defeated but now I think I understand!! im currently a software engineer in test but I'd like to prepare for my future possibly as a swe. one of the videos I watched was choosing a pivot randomly in the array which had me like 🥴but this makes a lot more sense to me! kind of reminds me of binary search.

[@codeloners6820]

very understandable! you are amazing tutor! keep doing such a wonderful video!

[@adhamkhaled5399]

Wow, just amazing!! Thank you so much.

[@pinkymartini]

Oh man you are amazing. Clear explanation. You have rightfully earned a sub sir.

[@SatyaMantha]

This is the best QuickSort Algo I have seen in KZbin

[@carlostitlan]

I only knew quicksort is the fastest. Now I know how it works and how to code it. I also practiced recursion. Thank you very much.

[@funkyjunky845]

Yeah, that's a tutorial I was looking for!

[@K.K.M.DEALWIS]

your explanations are amazing

[@maryamz215]

First time i actually understood this algorithm. thank you

[@yaweno9555]

Very well done video on quicksort with Java. I'm impressed with John as an instructor from this first video of his I watched. John explains things in a way that is easy to digest and comprehend. I came upon this one after a demo of quicksort in a Learn Haskell video. This review helped me better understand some of that foreign syntax in Haskell. I do have to say that Haskell does the quicksort in far fewer lines than Java.

[@thedevbek]

@Coding with John, You did a great job on this tutorial. Thank you very much.

[@francksgenlecroyant]

You're amazing John, i am your new subscriber! I'm enjoying your content

[@stephanieezat-panah7750]

Awesome tutorial. thank you!

[@sarkaholendova9080]

You have helped me get through University. I appreciate you so much! :)

[@kymberlicodes]

This was so helpful! Thank you so much.

[@jondevlin4754]

Just watched two of your videos … have taught gifted grade 12 CS for years … now switching from C/C++ to Java …have just watched a couple of your videos … your communication is exemplary…so clear …

[@timurboltaev8688]

Thank you, John. Great explanation.

[@liatsahi]

Thank you for this explanation. thanks to you I understood brilliantly

[@kesarscorpio]

pointing the pointers points a pointing image in my head :D thanks for the explanation, very useful.

[@ishank7239]

When I watched this video for the first time, I was a bit hesitant to implement it this way. It was because of the nested "while" loops. It took some careful observation to understand that although there are inner while loops, we only go through the array once : O(n) Thanks for this clear explanation. 🙏🏽

[@amandapanda3750]

Really Appreciate these videos ☺

[@ntc3337]

This is great thanks! I've 4 years working experience but I'm studying for job interviews and I always find myself having to go back and learn DS&A stuff haha

[@kiranmayiippili6058]

You are too good. Wonderful explanation. Thank you tons.

[@kermitaner]

This explanation of the quicksort algo is the best i've seen so far on YT. Maybe i try to implement it in Cobol on our mainframe next week, just for fun :- )

[@samuelevans9115]

your videos are amazing!

[@schwaccc301]

Best ever,! Thank you so much for sharing this!

[@eugeniatatarchuk9641]

Thank you so much for your video! Everything is clear :)

[@AbdurahmonMirobidov]

just mind blowing , well done

[@odaia.7519]

Wow that is so advanced and i understod, liked it. Thank you so much, hopfully one day would be able to create something like this after finishing my Study soon in 2 monthes

[@KoushickSudharsanam]

Thank you man. you are the best.

[@emerson3070]

Needs a few re-watching lol Thanks John!

[@_Anna_Nass_]

Wish I had found this channel earlier. Great explanation once again, thanks!

[@InvinciRD]

agreed 100%

[@heartoutloud7498]

Damn John. Im loving your videos man. You really clarify stuff which other tutors just ignore, that creates a lot of trouble. I actually would ask you if you could clarify the concept of returning. Plays a crucial role in coding and I miss the point of returning ometimes: "Does return close a program?" What is the point of returning is the return is void? " "Why do we have to return?" Thank for the great videos!

[@jonathancabral8124]

I was having difficulty to understand the logic behind the implementation and your explanation it’s really great. There is just one thing that I do not fully understand that is why choose a random pivot it’s better than always take the last or first element.

[@Urbaez22]

Excellent video and explanation. I just add that when facing a StackOverflowError in Java, you can adjust the -Xss parameter to the JVM when booting up, to a larger value. By default I think it's 1024KB but can be set to whatever value necessary.. Thank you for your content..

[@hallosf1396]

We're waitin for Heap Sort !! And thanks for your effort

[@adokat]

Extremely helpful, thanks.

[@checkmate2625]

Hey man, Data structures and algorithms will become an interesting topic if everyone teaches like you.👍👍

[@anupamjoshi6077]

Thank you so very much for helping me understand the concept as well as the implementation

[@anupamjoshi6077]

Also can we reduce one extra swap inside the while by surrounding it with an if condition which says that left pointer is not equal to right pointer

[@abhishekkmr549]

Your channel is true gem..

[@santoshpalli4432]

Great explanation Sir, Thank you so much..

[@svalyavasvalyava9867]

Your videos are educative and really fun to watch. Thanks for all the effort you put into the content!!! P.S. on 8:16 the rightPointer should point to the pivot element. However, your implementation was perfectly correct so this is not a big deal.

[@CodingWithJohn]

Thanks! And you're right, I suppose that is off by one between the implementation and the demo there. The end result should be the same either way.

[@__nitinkumar__]

Thanks for that, I was implementing and had written the logic as int right = end -1; but in the John's implementation I saw it being as int right = end; // was a little confused here.

[@scottyp02]

Great video!! Super informative

[@shahdadpeykani7641]

Thank you sir, finally I could understand completely after watching 10 times 😂❤️

[@amarsarkar4925]

Was waiting for this ❤

[@phekev]

Me too. I'd recently watched the merge sort video and wanted a quicksort to compare it with.

[@dondigidon1633]

Really like your channel! Keep going, your are the best!🏆🏆🏆👍

[@quitchiboo]

Honestly the best tutorial on quicksort out there! I'd like to add: You don't have to use a number from the array as a pivot. You can calculate the median of the array and use that as the pivot, to queeze out even a little more performance.

[@TuanBuianonymous]

how to calculate the median of the array?

[@quitchiboo]

@@TuanBuianonymous Count how many numbers you have. If you have an odd number, divide by 2 and round up to get the position of the median number. If you have an even number, divide by 2. Go to the number in that position and average it with the number in the next higher position to get the median.

[@thanhtungtran8249]

@@quitchiboo in an unsorted array, the median could be any number, such as the highest or lowest number, so it does not make the algorithm that much better

[@rasa7778]

Thank you very, very much for your videos, they are very helpful for me. You are doing a great Job. ♥♥♥

[@zeuss_2122]

Thanks alot. My request was answered.

[@natnal9587]

As usual, easy way to understand. I just got out of the class and our professor said it better to use the median for choosing the pivot. while choosing the pivot would it better time complexity if we do (left+right /2).

[@marq_8976]

Excellent explanation.

[@jimwang8997]

Thank you John, good job! in the second while loop, not need leftPointer < rightPointer, because the first while loop already have same code.

[@UnfinishedYara]

I tried it myself and without leftPointer < rightPointer in the second loop you find that the array values are flipped, so the first one becomes the last and so on.

[@nobleman2704]

thanks for all, btw in jdk library when it comes to sorting, it uses DualPivotQuicksort sorting algorithm

[@wbarbosabr]

I think I figured out what's wrong: When the chosen pivot is the highest number it'll end up in the wrong position when swapped from highIndex position to leftPointer position in line 61 of the code provided as in 2022-JAN-17. I solved this by substituting the said line for the following code... Suggestions for prettier, faster solutions are welcome! if(array[leftPointer] > array[highIndex]) { swap(array, leftPointer, highIndex); } else { leftPointer = highIndex; }

[@CodingWithJohn]

Great catch, I think you're exactly right! I put in that change and ran a number of tests, and it seems to fix the issue where that last value could be out of order. I've updated the linked code with your change, and will add a pinned comment about what the issue was (and give you credit of course). Thanks for checking it out!

[@__nitinkumar__]

Hey Wilson, Correct me if I am wrong. From the fix I understood that, it is only required if you are taking the pivot randomly. Else there is no need of it. One suggestion would be from the readability point of view: _array[highIndex]_ is nothing but the _pivot_ variable so why not use that. :)

[@wbarbosabr]

@@__nitinkumar__ Yeah. In fact, you can just return highIndex at that point instead of assigning it to leftPointer and then return it.

[@TuanBuianonymous]

in this video, int rightPointer = highIndex => so that's why no need to check if(array[leftPointer] > array[highIndex]) . But in the source code rightPointer start from (highIndex - 1) so need check if(array[leftPointer] > array[highIndex]).

[@andrescastaneda1208]

@@TuanBuianonymous Agreed. I was just about to point this out. I prefer to just start the right pointer at the high index so there's no need for this logic check. Seems cleaner.

[@coordinator3039]

I really needed this for my Pokemon practice code project

[@dmitricherleto8234]

Thank you again for a great video

[@elmehditalbi8972]

Hello, John. Very detailed video! Thank you so much. Can you please do a video on generics in java as well ?

[@kunalkheeva]

Thank you john, I just need more clarification on time complexity

[@interstellarguy]

Thank you John