I coded a Leetcode clone (it's easier than you think)

I coded a leetcode clone (an online code judge application, not literally a leetcode clone). I walk through how I did it, including the backend, frontend, and the process of executing test cases.
🚀 neetcode.io/ - Get lifetime access to every course I ever create!
Checkout my second Channel: / @neetcodeio
🧑‍💼 LinkedIn: / navdeep-singh-3aaa14161
🐦 Twitter: / neetcode1
🥷 Discord: / discord
0:00 - Intro
0:20 - Backend
3:02 - Frontend
4:45 - Adding a problem
7:58 - How I did it so quickly
8:49 - How did I git gud?
#algorithms #neetcode #leetcode

[@NeetCode]

What do you guys think? Not bad for a leetcode monkey eh 🐒 Try it out: neetcode.io/problems/dynamicArray Or view the full list of problems under the 'Basics' tab: neetcode.io/practice

[@vs3.14]

This is amazing. Can't wait till your quizes portion of the practice problems are over. I am currently following NC150. After that Leetcode and the back to NC430. It helped me so much. Thanks again for your hard work!!

[@adrian333dev]

Can we access to source code of this project?

[@bubblesort8760]

Sir this is absolutely astounding. Great work. Commendable

[@beodwilson5257]

Hey Neet! I can help with customizing the monaco editor to look like vs code. Let me know if you are interested I can hop on a quick call to walk you through how it can be achieved.

[@indrajeetv8878]

Can you please create a top 250 important problems, it would be a huge help!

[@siyamafroz]

Bro got bored of solving leetcode and decided to make his own leetcode 💀 Keep it up man

[@marcusplenty1153]

Bro solved leetcode. Difficulty Level: Medium

[@ujjvalw2684]

​@@marcusplenty1153ouch

[@recursion.]

I already know neetcode will be the future of leetcode.

[@jl_117]

im gonna do this too because both working on an unrelated project and doing Leetcode is too much work when also job searching

[@learningalgos614]

Now please implement the sliding haircut algorithm in O(N) time and O(1) space

[@amroulouay6819]

Given two integers num1 and num2, return a leetcode clone including the all the backend (difficulty: easy)

[@notdarkangelu]

Given two String s and t, return a girlfriend of primitive type

[@harshitnagila9832]

@@notdarkangelu function(girlfriend){ print("In dreams");}

[@notdarkangelu]

@@harshitnagila9832 ClassNotFoundException : Can't find girlfriend even in dreams

[@harshitnagila9832]

@@notdarkangelu import util.dreams.girlfriend;

[@amroulouay6819]

😂@@notdarkangelu

[@saadahmed688]

I am making a website for competitive programming too. But since I am doing this for educational purposes, I wrote my own judge from scratch which uses apparmor for isolation, bash and python for judging and C++ for output diffing. I have also written a judging microservice in Go so I can scale it by simply adding another worker node

[@vihan1873]

can you share the github link if possible ?

[@iNoxux]

could you share some insights how did you do it?

[@vaishnavghenge]

Keep going mate! you're doing great stuff, I must admit.

[@petyap7600]

Watching only yours video about algos. Thank you mate! Keep it up!

[@akashdey5637]

Great work man, keep it up

[@ducthinh2412]

wholesome content as always! When would you say you were able to consistently solve unseen leetcode hards, like after how much practice?

[@JosephChancey]

Could you please make a course on this for your site? Would love to see a simple project put together to explain this in more detail. I think the hosting it yourself part is the most intriguing.

[@mirrorinfinite5392]

Would love for a longer and more detailed video regarding the problems you faced/ any interesting things that came up! Really cool video, staying tuned for more of these

[@alienfunbug]

I love the part where you discuss the shortcomings and thought process/option weighing. It definitely feels like a good entry to the system design questions.

[@VivekDudani]

Great stuff man. You are doing simply amazing. It would be very interesting to know how you self hosted it? Like you are running your own spare machine as a server or somewhere on public hosting … Thanks again for sharing your passion.

[@business_central]

dude, you are definitely incredible 😂🙌

[@adityaparab4314]

The way you inspire us every single time is exceptional.💯👑

[@bephrem]

This is a super interesting video since I've been looking at the same problems for the past few years.

[@YK-fg5ne]

You need to make a whole course on this exercise/practice. From backend to front end. I would pay for the course.

[@amritakesh]

Just a smol suggestion, can you add a note section next to each question where we can write something done like "revise", "solve another way" or some clue that will help us revise

[@pirateg3cko]

Great stuff, neetcode! Keep it coming 🔥

[@NeetCode]

It's been 30 seconds how did you watch it already 😲

[@VidyaBhandary]

Not sure of OP but first your video is an automatic like first and then continue to watch 😂

[@pirateg3cko]

@@VidyaBhandary you said it! 😂 I commented then kept watching. I stand by my comment.

[@VidyaBhandary]

@@pirateg3cko Exactly 💯 🤣😅

[@aka.theos.]

Hey great content you honestly make me want to leetcode more and I have only been doing side projects and the comment about next js app router hits home I picked it up so fast and it seems easier to me that the page router

[@jafarjuneidi7585]

“One of you assholes is gonna try to mine bitcoin on my VM” had me dead 💀😂

[@Yopperpo]

next neetcode video: I coded my own programming language (it's easier thank you think)

[@rajenderkatkuri7642]

Dude BTW what framework did you use? Angular again? 😢

[@Sranju23]

Lol - my fav part ‘The Backend’ 😂😂 Gotta admire the humor. 🙂

[@user-2802cvsfkj]

Thank you so much. I got hired yesterday. ❤ Thank you so much.

[@ravenloue]

Great video! Very impressive results. I haven't read through all 170+ comments because I'm too lazy for that; however, your issues with the editors looking different intrigued me. So I started to play around on the Monaco playground to try to understand whats going on. It seems that for VS Code, the team added more token types for specific instances; whereas Monaco is very simple. If you want to get the Monaco playground to look more like VS Code, then you're going to have to edit the default setup of the language file to add more tokens. It seems easy enough, but it definitely would be a tedious task.

[@NeetCode]

Yeah that's exactly the issue that i ran into! So annoying.

[@Zefn1x]

Mah man keep the good stuff coming! Also you got any plans of sharing your tech learnings as things itself?

[@RhythmSharma00088]

nice video Bro Those leetcode hard does payoff

[@Cruzylife]

This was a pretty cool video

[@Sandeep-zd6dq]

How can we contribute in this project 😎 btw kudos to your hard-work, we all know the pain of configuring the webpack 😂

[@jamesisaacson6414]

You know we appreciate videos where we can see you talking instead of just listening to your voice

[@johnappleseed2578]

I built a web based YAML editor with Monaco and had ALL the same issues. So glad I’m not just dumb like I thought

[@ashminjayson3978]

Hey, awesome work 🍻💖. I had a question as to how you handle the testcase validation of testcases with multiple right answers. Are you just comparing the user's answer to all possible cases or is it through some other method?

[@user-ew6ve1zq1t]

Thanks NeetCode, your website has helped me escape samsara! 🙏💎🇧🇯

[@sayanghosh6996]

for custom test case you may choose (design decision) to not show correct output and only their code output.

[@user-oo9nd7qh9k]

bro is it possible to get mentorship from you? for cracking google or such companies?

[@ShubhamSingh-vh1vw]

Cool, that is really cool!

[@WalterGordyCanada]

Maybe for the submissions where it calculates how you did compared to others it could run on standard easily repeatable hardware or benchmark the solution against another known problem each time. I never know if my algorithm was great or just had a good run on the hardware on leetcode.

[@yoursandeep]

This is what I wanted to ask what backend judge0 ( I infact did a poc but was not sure if i should use this), you answered it. This helps.. Thank you very much !

[@brandonlee378]

Hey, do you have a github for your projects?

[@dinoscheidt]

I wonder if web assembly is good enough now, to have a wasm version for these languages run in the browser and only validate on the server when a potential solution is found. Would be “zero” latency.

[@yfjsdgzjdnfn]

Happy Teachers Day, NeetCode

[@mr.mystiks9968]

Honestly Judge0 makes this project 10x easier when you don’t have to know how the entire repo was designed.

[@NeetCode]

I read a lot of it's code, it's actually simpler than you think. It mainly makes use of a CLI tool that handles most of the security (isolate)

[@gyanaranjan6526]

That Judge 0 thing was bothering me one year ago I searched for similar things but couldn't got something so I made some container things with docker and kubernatse some how managed it but it has lots of flaw.

[@TheCricketChap]

Osum stuff 🔥👌

[@nagendradevara1]

Angular's batteries included approach lets us focus on our business logic and saves us time.

[@yashsolanki069]

How much does running judge0 self hosted cost per month and what configuration you are on for instance? I was thinking of doing the same and thought i could self host judge0 repo to render cloud on 500 ram lol. Definitely have to work around this. This video really helped clearing some point. 👍

[@pheezus]

Laughed at the app router stuff lol. Good ol' Angular

[@prajwalpawar3110]

when will i ever be able to code like you .

[@himanshupoddar1395]

I watch your videos a lot, never thought that this account was run by an Indian/person from Indian descent. From your accent, it never seemed like so.

[@NeetCode]

🤠 🇮🇳

[@atharvapatil4247]

From solving random leetcode problems to completely shifting to neetcode I have upskilled a lot

[@kollpotato]

4:04 medion of two sorted arrays is the only hard leetcode problem that i have solved lmao

[@tah-seen]

Could you please curate a playlist for data structures and algorithms for a Data Engineer.

[@husseinkizz]

Man keep doing these videos, they're very indepth in technicality and nice, though I think showing your face may kinda change things, I thought you were older, cause man, you know a lot of suff, I like it when I see you as an older jade master hahaha!

[@NeetCode]

Yeah this is one of my favorite videos and it wasn't even a pain to edit it, so I def wanna do more like this

[@husseinkizz]

@@NeetCode Yeah keep doing this awesome work, we like it!

[@user-ff2ep5kk5i]

Beautiful stuff, can't wait to test it!

[@Lonelytraveler8236]

Nice video, i am curious about two things : how do you manage time and memory limits while running all test together and handle multiple format correct answers ?

[@bossgd100]

curious about the answer also

[@saadahmed688]

He's using an open-source judge which handles it for him. I wrote my own judge and I used rlimit for time and manually checking memory using a bash script for memory. If you place memory limits using rlimit (which is what ulimit uses) you can't send a custom signal to the terminating program to differentiate between a SIGSEGV and a run-time error. I have oversimplified a lot of stuff here btw

[@Lonelytraveler8236]

@@saadahmed688 i read the open source judge api and it calculates the time for the overall submission. And since neetcode is running all tests in one sub how can he verify the constraints for each test. That was my question, thanks anyway i got a clear understanding how judges works.

[@HSBTechYT]

Didn't know something like judge 0 existed lol. Had to write my own Judge 0

[@asedifo]

Do you have a longer writeup on the security side of things beyond just running it in a VM? Things like containerizing within the VM, blocking outbound ports, blocking the ability to change outbound ports, limiting subprocess code execution, etc? Thanks!

[@bossgd100]

i am curious about the answer also

[@Supakills101]

This is more devsecops so probably he won't cover it.

[@saadahmed688]

The open-source judge he's using already takes care of that

[@mr.mystiks9968]

judge zero already handles this. it uses docker containers with least privileges, and allows you to set a time limit for how long the code can run. it makes the entire project 10x easier.

[@Imstupid-ni3we]

So did you use some AI tool to generate test cases? Also, you mentioned about the front-end part and how annoying it is, it's pretty much the same story for me. I have a few side project ideas but I always get demotivated just by thinking about the front-end part. do you have any advice on that?

[@ram8551]

Hey @NeetCode, thanks for the video. Just curious what tech stack you used to build the clone? You mention angular for frontend but what about the backend?

[@tashima42]

I think its just judge0

[@Sranju23]

he has explained it on his one video - kzbin.info/www/bejne/aniYpWR-rK2EepY&ab_channel=NeetCode

[@nhan2518]

I am really interested in how to make it!!

[@krtirtho]

Developers doesn't fear Algorithm & time-space dependencies Developers fear application dependencies

[@deathz0ne]

broooooo......NEET🍻..............Mindblowing 🤯🤯🤯 🤟

[@myke6972]

Hey Bro! Do you think it's possible to make a HTML CSS JAVASCRIPT compiler with output, and test cases?

[@alamicrodev6526]

I hope one day I can get as smart as this guy

[@Spud_Lite]

recursive stack visualizer when?

[@the_npc_artist]

When you see a piece of code you like, You yoink it... that cracked me up dude 🤣🤣🤣🤣

[@edavar6265]

Can you solve Duplicate Zeros and some other bunch of insertion questions? I really struggle to understand them.

[@rahuldwivedi4758]

4:15 For us,the front end developers, adding theme is as easy as for you solving a leet code problem is.

[@coldsky_]

I felt that haircut 💀

[@bossgd100]

The other dev who needs unit test is your future self

[@machmachine]

wholesome watch!

[@naksuy]

when can we test this 😅

[@isaacjon]

Where is full tutorial of building this application?

[@rabbyhossain6150]

what if you make this project open-source? so, people can contribute

[@ashu3403]

Maybe integrate system design as well

[@berkay2410]

Not too long ago, I sent you an e-mail about localized pricing and you replied in an instant sir! But then, I couldn't hear back from you :(

[@ramboli4118]

How do you store the progress of users? like their code?

[@anotherEmail475]

Nothing is hard as long as you have time and money to do what you want. Programming is different for everyone and people learn with different pace. You sounded like someone putting above others. Don't be disrespectful cause there are plenty of people copying with imposter syndrome and you are actually making them feel bad. Other than that keep up a good work

[@EzraSchroeder]

@1:00 how did you find judge0 ?

[@MancySaxena]

Take a bow man! Did leetcode, went to Google, left Google, made another leetcode!!

[@ShruthikRavula]

Bro, could you just recommend what to and where should I learn to just understand what you are telling

[@amono770]

I don’t know why but u look smart af

[@AshishSinghh]

Golang solutions as well please

[@heatchecknyc2142]

Are personal projects really more important than leetcode

[@Cygx]

This one man is an absolute menace for taking on a multimillion dollar company and doing it better.

[@HimanshuKumar_24]

yahan ek medium level ka question nai banta , bhai ne Leetcode hi bana diya.

[@nio.ritesh]

yes i can help you with customising monaco theme

[@alangamer50]

Leetcode be like: Make an algorithm to reverse SHA256 in O(n) time and O(1) space. Medium difficulty (discussion section thinks it should be labeled as easy)

[@AnhNguyen-vu7mc]

Was thinking instead of using judge0 we could use a docker image for each language and have a worker pool to execute submissions

[@ashwinsnmv]

This is mot the example of a developer. This is a plug and play engineer. As soon as you hit a road block, you'll be stuck. A good developer can solve leetcode problems but the other way is very rare.

[@XEQUTE]

hey dude , You can either : - make it open source and hire and get people to work through people through pull requests with bounties ( do first , get paid first ) - hiring through your channel , community post with google forms or any form solution you like. ( making your community stronger ) - hiring professionals from freelancer. I'm up for the frontend job if thats okay with ya .

[@bossgd100]

- create a dao with a token

[@adityabanka_iso]

Absolute Chad

[@clouddrive6833]

My head got exploded

[@Ajeetkumar-uo4hf]

You are amazing ❤

[@NeetCode]

❤️

[@SomeoneAlive90]

Why did I read “I coded a NeetCode clone” and was so confused that why would he clone his own website? 😂

[@nithin3476]

you can use docker

[@abhishekkumar-fw4nm]

Make it open-source people will love to contribute

[@bephrem]

No the Monaco editor syntax highlighting is annoying. I went through the same thing. I switched to CodeMirror because of how complex it was to add your own highlighting config.

[@Zeiyon]

Why did you choose angular? Just curious.

[@themagickalmagickman]

Its what he used at his job so I assume he just kept going with what he knows

[@Zeiyon]

@@themagickalmagickman Ah, I mean he has a course on react so I was curious why he switched back to angular

[@NeetCode]

Yeah I started neetcode.io with angular 1.5years ago. In hindsight it was a mistake and I should've used React, because it's simpler and more ppl are familiar with it so it would be easier to hire for.