Subarray Divisibility (AtCoder) 

Codechef may long challenge Chef and bitwise product. After contest ends*

really cool technique. These type of questions shows the beauty of cp.

You are only and only genuine programming youtuber. Most of them turned into late night shows.

Whats the logic behind : "answer += cnt_suf[suf]"

nice development of answer

The forwards algorithm is very similar to your backwards algorithm. You only have to change two lines after reversing the loop. power_of_ten = 202 * power_of_ten % MOD; // 202 = 10^-1 (mod 2019) suf = (suf + digit * power_of_ten) % MOD;

Hey bro please make different series full of practice questions specially dedicated to graphs and recursion please.....

Errichto can you make a video for those who cannot understand blogs ... i mean how to learn then ? via videos ?

thank you very much : )

How to approach constructive algorithm problems?

could you do codechef may challange 2020 last 4-5 questions they are pretty good questions ....it would a great help

Very nice Errichto. But why do use MOD here: power_of_ten = 10 * power_of_ten % MOD; ?

make nanobots in may long challenge code chef

DP on trees please!

pot = 10 * pot % M, why do we have mod M here?

Want to know why power_of_ten also need to mod 2019? Thanks!

doubt: line 20 => power_of_ten = 10 * power_of_ten % MOD, why we have to take MOD?????

Codechef contest editorials, please give this a few likes so that erichitto can see!

10:52 , shouldn't you check if(s[i]='0') you cant add answer to it? ex: 2019 will be 2 not 1 because 019 and 19 have the same suffix edit: lol my bad, i didnt read the problem constraint carefully

Really Needed To Understand This Problem For A Long Time. Thanks Errichto 🔥

8:59 said every programmer

Thanks errichito for tell about codeNcode... He is very hardworking to help beginners like me

but if I have a sample like s="111" and number is 2 then the provided method will output 3 although it should output 0 because no substring is divisable by 2 , can anyone explain to me if I 'm wrong ?

Let us consider s="019" , the value of suf=19 when we are at "1" and after that cnt_suf[19] will be one , then for "0" again suf value will be suf=19 and now answer will be incremented , but actually the answer should be 0. @Errichto can you explain this ?

Is there a way to handle the case when the modulo is not coprime with 10?

Sir I didn't get that how you wrote count of suffix equal to answer ...? Anybody plzz explain

Thank you for this video I am really struggling for the understandable logic😁

bro u r so down to the earth person. i did'nt watched this video but liked it, because nice people are very less in the world.

A day in the life of errichto

Please teach data structures and algorithms from the beginning & also please teach us how to master all these through competitive programming . Please. Guys please like this comment if you are a beginner & want the videos on these topics

can anyone explain me why he is adding cnt_suf[suf] to answer.he should keep track of numbers only divisible by 2019 right

Thanks Errichto -- very clearly explained, I always learn something from your videos.

Video was cool but still didnt find any reason why from prefix it should not work. This is 100% unclear to me.

It seems that Code NCode doesn't exist anymore :(

how to solve the harder version of this problem when M is not coprime with 10, eg, like you showed with M=50?

what to do if k=8, it is not coprime with 10.please reply

Great video! Helps me a lot

Morse Code - Codeforces

Hi Errichto, is it possible to cover the solutions to 2019 Kick Start Round A Contention and 2019 Kick Start Round C Circuit Board problems. I am struggling to understand the analysis provided. Thank you.

Hey , can you cover the may Codechef questions . The bitwise question was still easier but after that the questions were really really difficult. Specifically please cover the question on sorting vases and and the one on buying strings. The editorial talks of aho corassick and building automatons but can it be done easily ? Would like to know your approach. Please do if possible atleast one of them

Don't you actually have to add cnt_suf[0] to ans? It seems to me that the subarrays that are already divisible should count 2: once for all the combinations among them (as with any other) and once for themselves.

*PLEASE ANSWER ME* Hi Errichto, I would like to know something from you that is right now I am learning node.js and I wanted to know that what is the right time to start with comparative programming for interview perpose. Should I learn node.js completely and then start with competitive programming. Or should I start right now along with my node.js *By the way I am learning node.js on my on. SO PLEASE ANSWER ME.

Do leetcode hard problems boil down to discrete math? How important is discrete math when it comes to solving Coding problems?

Hey errichto would love it if you made a video on open.kattis.com/problems/matrica very confusing for me since for an efficient solution you should only calculate the required colums.

How Can use this method for divisiblity of 4 . codeforces.com/problemset/problem/628/B

Alternatively you could reverse() the number string first and then use prefix sums.

I think you should give a shoutout to “take u forward” also. He is creating excellent codeforces editorials.

Hi Errichto. Can you please explain why for String s = 7325 and MOD = 2 code gives ans as 6 but it should give 3 ?

Thank you Errichto. Great video! As all others on this channel.

which IDE for c++ you personally use

why does M has to be coprime with 10?

Can you make a video on segment trees and fenwick trees?

Saw you solving "221.Maximal square" the other day. It would be interesting if you can solve "85.Maximal Rectangle" which is similar but a lot harder. The solution with histogram is very cool.

Poruszyłbyś temat maximum agreement subtree problem?

Thanks for doing this videos

codechef long challenge solution; after contest ends;

I didn't understand answer += cnt_suf[suf] Is the vector initialised to zero in the beginning? Thank you

best teacher ever

hi i dont understand line 23 and 24 . what does that ++ operation will do in vector ?? sorry i dont kow c++ im a python coder!! it will be good if some one covert the same solution to python

Very natural and excellent explanation. Thanks Errichto! But you are making me lazy though.

Leetcode trapping rain water 2

please make video on string theory. string algorithm and some question based on them ..thanks for this video.

I just copied your code and tried 20192019 here we should get answer 2. As 2019 and 2019 both subarray are divisible by 2019. But it gives answer 5. Where is the problem? Am i gettung it wrong?

I assume when we think about time complexity we don't consider some functions. For instance the % operator follows an alghorithm to calculate and return value but we dont consider it in our code's time complexity. My question is which parts don't effect time complexity strongly that we can ignore them?

Share discode link

Please solve Codechef Challenges

It will always be more helpful. if you do a dry run of the code. :)

Needed it thanks

Can you please make a video on this problem I just learned fft and was stuck at this problem for long it would be really helpful codeforces.com/problemset/problem/993/E

Can we also find the multiple of 2020 or any numbers by this method will it works????

Challenge: Show shortly that your solutions on problems will pass every test before you submit !

IoI prepration path algos tips

Is it pigeonhole principle ?

Hey Errichto I have a question, I don't know c++ lang but I know python but on every competitive coding sites/platform I have seen the coders mostly use c++ infact you also (some also use java, like petr) I know the reason behind using c++ it is very fast, vast STL library etc. and on the other hand Python is slow and there are various other cons about it. So what do you suggest should I learn c++ or go with python or learn any other new lang which has both the combination of c++ and python language (like which will help me in CP and as a developer also in future). There are various news coming about different programming language which will replace python so keeping all this in mind what do you suggest, plz reply if you see the comment and I thought this would be the right place to ask my question as you are very active here. Thanks.

It would’ve been great if you added some background music such lofi hip hop or whatever