Codeforces Round

[@jeetganatra7977]

Please regularly upload... All the contests.. Even if you don't win it 😝

[@kushagrasahni9708]

I solve E this way: I stored in and out times of all nodes. Then in each query, pushed the in and out times of the parent of every vertex in the query in a vector of pairs. Then I sorted the vectors and iterated through it to check if every node is an ancestor of the next node.

[@NishArcturus]

No need of vectors man if you have in and outs then you can check ancestors in O(1) just by comparing, they have a whole section in CLRS on the same IN(CHILD)>IN(ANC) && OUT(CHILD)

[@sanchitkumawat3803]

how did u solve problem F in so less code than its editorial and yours is easy to understand as well.

[@mohammedamaan7351]

Thank you so much man. You are a legend. Your work is helping me so much. Please be uploading videos like these in the future contests as well.

[@NishArcturus]

Man I can literally watch your vids all day😂

[@AmitKumar-kj6hh]

Thanks William lin , your video helpful for us 🙂

[@LyTran-tj7sy]

Please continue this series. It helps us a lot.

[@blueexorcist4300]

Not only you are an amazing coder but also you explain things very well... please please keep doing this!

[@santhoshdeepu4293]

Bro i can't even understand one code solution and i know java basics and oops and currently leaning DSA(SLL,DLL,CLL, stack,queue) now learning tree can you suggest me how to increase my programming skills.

[@akshar4548]

If possible please upload videos after every major contest ( also from codechef) so that we can learn from u and improve our mistakes....thank u brother for doing this ❤️

[@georgielee3690]

yo what keyboard do you use? you should make a setup video ^_^

[@tmwilliamlin168]

It's a random mechanical keyboard... Yea sure I might show my physical setup one day, it would be pretty short tho

[@cqtShadow]

love your video, and just want to be like you

[@tmwilliamlin168]

Doing a lot of practice is the key for anything.

[@omar-elaraby]

Good job bro, that was helpful. And best wishes in your next IOI :). And could you share with us your road map of your early practice ?

[@tmwilliamlin168]

I didn't have a roadmap

[@josephwong2832]

love these solutions

[@ritwikchakraborty1702]

William can you tell me...how to learn when we are doing some code..do we should see other solutions for improvement or any other way??

[@tmwilliamlin168]

Yes, you can learn a lot from reading others' codes

[@ritwikchakraborty1702]

@@tmwilliamlin168 thaks Willam...I am also in your discord...if any doubt comes to me...I will take help from you obviously

[@shashikantpunia9019]

in 2nd question, you said no of strings whose first character at position i is n-i-1, but for n = 5 and i = 3,the no of string whose first character at position 3 is 4, n-i-1 is 1... may be i understood it wrong ! plz resolve mine doubt...

[@tmwilliamlin168]

Why 4? Can you list out the 4 strings?

[@vaibhavpandey5615]

thankyou lin ,we need this..

[@ibroq1]

i just came here to hear sound of typing level 9000

[@andremanada5175]

i used dfs to calculate the path from u to root, and put the path on a set, then checked for every node if it or the parent were on the set, got tle on case 58

[@tmwilliamlin168]

Consider a bamboo and a bunch of queries, all of them with the deepest node.

[@shmaestro]

Incredible speed! Question on A: why take (b-a) instead of (a-b) in the calculation - just trying to understand the intuition on this..

[@mohammedabutair4627]

if(a

[@tmwilliamlin168]

Each time you add 1 to a, (b-a) decreases by 1.

[@shmaestro]

@@tmwilliamlin168 Cool, thanks!

[@naranbat.m8026]

Pls tell me, why u use GVIM, dev-c++ ide is not better? What reason is why you choose GVIM?

[@unuuunudelger6779]

Thank you

[@aniruddhashrikhande1178]

Regarding question F, how can we prove that it is optimal to always have the K equal numbers as some pre-existing element of the array? Why can't we have K equal numbers which were initially not present in the array?

[@tmwilliamlin168]

I actually haven't thought of that, but its proof is related to this proof: math.stackexchange.com/questions/113270/the-median-minimizes-the-sum-of-absolute-deviations-the-l-1-norm Basically, if we increase a elements and decrease b elements to become x, if ab, x-1 will give a better answer.

[@teji7723]

I understand 67% of what he is saying. C++ language can be spoken!

[@jonathanlouis6776]

You inpired me to create a channel youtube like this XD. Thanks for the explanation !!

[@srikarummineni307]

Sir please upload them regularly Was missing this very much Thanks a lot..!!!

[@mayankkumarprajapati1763]

You are doing awesome work bro..

[@TahsinAhmed-yj9ns]

thanks for making this

[@rahulanandyadav1039]

Can you tell your coding environment setup? The program you use and other configurations

[@utsavpati5855]

I am a big fan of yours and please upload solutions regularly

[@DharanAditya]

You are doing great job bro. I am regularly visiting your channel. I have difficulty understanding the second problem kth string even afternoon watchiny your explanation multiple times. Can you help me

[@ishansourav4142]

bro can you explain why did you take xor of anc[u][i] & anc[v][i] ?

[@mohamedSayed-lr4xs]

could you please tell me what kind of keyboard you are using ??

[@tmwilliamlin168]

A mechanical keyboard

[@MD-hx3wf]

Hi, Which keyboard do you have?

[@tmwilliamlin168]

Some random mechanical keyboard

[@MD-hx3wf]

William Lin - blue switches I assume? :)

[@aditya_jain]

Thanks and keep going

[@suryakantasahoo9935]

Keep it up man, helps a lot!

[@yinghanma1314]

Could you also post some explanation video about quesitons in leetcode weekly contests?

[@tmwilliamlin168]

Yes, for LeetCode weekly contests, I don't separate the contest and the explanations

[@bhaweshmadhwani1801]

Thanks man🙌♥️♥️

[@scoopedcontent]

PLEASE make a video on complete road map for competitive programming......

[@tmwilliamlin168]

I don't know the complete road map for CP

[@yashveernathawat8154]

i was stuck at problem1...How should i improve? Although its my 1st contest

[@tmwilliamlin168]

That's normal for a 1st contest. Just do more practice.

[@pandalove6795]

Please explain how the code works in B.cpp?

[@vinaykumarbisht3008]

When did you started competitive programming?

[@tmwilliamlin168]

3 years ago

[@kabboghosh1853]

great teaching

[@visluck]

🔥🔥

[@sandipanhaldar61]

can you elaborate the variable s in prob D

[@tmwilliamlin168]

The start of the array (I shift the array circularly)

[@utsavpati5855]

And if possible please upload the Codeforces div 2 solutions held recently

[@tmwilliamlin168]

Sometimes if I'm unable to upload video solutions I will provide brief solutions in my Discord (link in the description)

[@sumitbisht4161]

Can you please be more clear while giving explanation cuz I didn't got nothing about kth beautiful string!!

[@divyanshubist8527]

I solved the first problem on my laptop but it exceeds time limit while submitting .how can I improve that? And pls explain what does checker's comment-"exit code is 4"means??

[@psw1]

You might be doing it using brute force. and looking at the constraints that won't paas. try to solve mathematically

[@tmwilliamlin168]

You need an efficient algorithm, and you might be getting runtime error

[@attrinh9412]

Thank u

[@kunal_chand]

Can u create a channel on telegram in which you post contest reminders before participating. It will be very helpful for us to follow along with your explanations.

[@tmwilliamlin168]

I'm doing that in my Discord server (link in the description)!

[@GannaJuiceEnthusiast]

20:50 how does considering whole prefix and suffix sum gives me the answer??, I mean their could be some elements from the left and some elements from the right, why does considering all elements gives us the answer?

[@tmwilliamlin168]

We consider all 4 cases, no elements from left/right, elements from left, elements from right, elements from both left&right.

[@GannaJuiceEnthusiast]

@@tmwilliamlin168 i got that, didn't read the qustn correctly...we can only change the greatest and the smallest element....my bad... btw thanx a lot...

[@khshgeiye4810]

C's solution is the interesting one

[@codeWithBatta]

bravo brother love you

[@DHANUSHrockyartist]

❤️

[@sihabsahariar]

Hey I'm a beginner. Why did I get TLE in this code? int main() { int t; scanf("%d",&t); while(t--) { int a,b,count=0; scanf("%d %d",&a,&b); while(a%b!=0) { a++; count++; } printf("%d ",count); } }

[@satyamkumar2820]

which editor is this?

[@saifu07]

Please upload explanation video of Kickstart A, Thanks

[@tmwilliamlin168]

Sorry, I got busy, and Google already has analysis for those problems

[@gopikrishna1551]

can u please explain D i am unable to understand it

[@AlexandrBorschchev]

i'm a beginner, please give advice i'm very interested!

[@organic2976]

Hey broly, make a video on your setup?

[@tmwilliamlin168]

Thinking about it :)

[@organic2976]

@@tmwilliamlin168 waiting

[@pranjalagnihotri6072]

Please someone explain me how to solve problem B, like how can we find the kth permutation directly. I looked into few articles where the idea was to use factorial number system but couldn't understand it properly. Please please provide few pointers

[@tmwilliamlin168]

In which part of my explanation did you get confused?

[@psw1]

@@tmwilliamlin168 your solution was perfect for this question in whichh there was constraint on number of b's and a's but what about a more general problem in which we need to find kth permutation of any general string

[@pranjalagnihotri6072]

I don't understand the idea behind doing ` if (k < n - 1 - i) `. Also why you started at n-2 and not at n-1?

[@classcure9769]

i didn't understand B.....I am a new coder pls help someone

[@crazymemes4080]

Give us some tips bro related to competitive programming 😬

[@tmwilliamlin168]

Practice a lot

[@gentleman4615]

Practice means only problem solvinG?

[@tmwilliamlin168]

Yea

[@muhamedabdalla2301]

wow, your solution in D is so beautiful, I solved it using dp, i hope that i can solve all like u but f break me :D, Keep going bro.

[@pranjalagnihotri6072]

Man you are doing so great solving problems till D needs much much practice 🌸

[@atishayjain9341]

It was easy I solved it as he solved it but he code is so less..... I don't know how he finishes the problem with a little code only where I wrote a very long code !!!! That's why I like him checking every ans after the contest just to check how did he wrote in sort

[@user-id5qq6ov3w]

Is it only me that doesn't even know what Codeforces is

[@halfblood_slayer5989]

Its a very light weight website and hardly breaks check it out

[@mohammadistiaquddin9543]

Which IDE do you use bro?

[@tmwilliamlin168]

GVim

[@abylay_gaming]

I hear frogs))

[@ak.pod31]

Why can't we just do a%b for the first one

[@sadmansakib007]

a = 5 b = 8 a % b = 5 % 8 = 5 But we need 3 moves to make 5 to 8.

[@akshaykumar-rv7gt]

Which ide di u use?

[@tmwilliamlin168]

GVim

[@dulanwaduge]

whats your keyboard?

[@tmwilliamlin168]

Some mechanical keyboard

[@adityamishra4458]

u did not explained educational round 84 i was waiting

[@tmwilliamlin168]

I got busy that day, sorry.

[@tmwilliamlin168]

The editorials are already on CF so probably not

[@thepenguin7324]

Happy 666e1 subs

[@mrinallumasudhan280]

I honestly think you can get a job at google pretty easily!

[@himanshunegi5228]

nice video sir can you please speak slow.😊😜

[@tmwilliamlin168]

I'll try to remember

[@akshat1234100]

Thank you