Errichto's blog

By Errichto, 2 months ago, In English

Target audience: newbies and pupils (rating up to 1400).
Group link: https://codeforces.com/group/yg7WhsFsAp/contests (hit "join" on the right).

Hi. Enjoy a series of 8 problem lists for beginners. The example topics are strings, arrays, math, and binary search. You are allowed to discuss anything with others, or just look up solutions online. There are also 3 exams, each recommended for a 2-hour individual virtual participation. Use the displayed order, e.g. take exam 1 after day 3. It all should take you 2 weeks of intense bootcamp-like work (or a few months if you take your time).

The problems were originally used two years ago in a Saudi Arabia camp. It's a mix of around 70 existing CF problems and 30 new original problems, mainly prepared by kostka, with some help from me and mustafabar. I asked them for permission to publish everything.

I will put hints to some problems in this blog (or in the group? not sure). Expect a few videos and/or streams for beginners too. You should also read two first chapters of Competitive Programmer's Handbook.

UPD: On Sunday evening I'm making a stream with explanations to a few hard problems: P8, P11, P18, P30, P31, P33. You can try it with hints first:

P08. Cashier
P11. Queens attack!
P18. Mountain peaks
P30. Temporarily unavailable
P31. Shuffle Hashing
P31. Shuffle Hashing, hint 2
P33. Thanos Sort
 
 
 
 
  • Vote: I like it
  • +251
  • Vote: I do not like it

»
2 months ago, # |
  Vote: I like it +19 Vote: I do not like it

Thanks a lot :D I'll try to solve all of them in the upcoming days

»
2 months ago, # |
  Vote: I like it +7 Vote: I do not like it

It is really usefull

»
2 months ago, # |
Rev. 2   Vote: I like it +1 Vote: I do not like it

Can those not in the rating range specified above not submit ?

Edit : Just checked, they can

  • »
    »
    2 months ago, # ^ |
      Vote: I like it +25 Vote: I do not like it

    You are allowed, but the problems should be easy and boring for you.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Awesome!!!!

»
2 months ago, # |
  Vote: I like it -8 Vote: I do not like it

you mind putting some more tough questions in there .

  • »
    »
    2 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    These are problems from a camp two years ago. The participants were beginners just after learning basic C++.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

This will help me a lot!

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

thanks a lot

»
2 months ago, # |
  Vote: I like it -28 Vote: I do not like it

Can you prepare another one for 1400 to 1600? I will be very helpful! And thanks for preparing this one. I will submit these problems.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Awesome

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

There is no problem numbered P17 in day 2

  • »
    »
    2 months ago, # ^ |
    Rev. 2   Vote: I like it +16 Vote: I do not like it

    Oh, you are right. I see now that we removed it back then because it required an algorithm that participants didn't know yet. It was 1041B - Buying a TV Set.

    I've renumerated problems.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thanks for this bootcamp Errichto , Can we expect more such bootcamps with a certain level up anytime :) .

»
2 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Reminds me of whenever I say I should start over competitive programming from the beginning since I am not good at the basics.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Hey!! Thanks a lot, it will surely help a lot.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Great , it will help us a lot.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I have just finished the basics of java and solved 100 URI basic problems and some hackerrank easy problems. need to read the first two chapters of "Competitive Programmer's Handbook". it will take some time. I will try it.

I have a question. if someone wants to try it after 3/4 months will these problems will be there?

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thanks a lot. Please arrange more Bootcamp or practice sessions like this for newbies.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Really awesome. I hope I enjoy and learn.I am really grateful for it.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

When I try to register it says "you are not allowed to enter", I am new to this platform. how to register for this.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

where will i find the editorial of practice problem of day 1

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Any hints/tips on how to solve P48 The line problem

  • »
    »
    2 months ago, # ^ |
    Rev. 2   Vote: I like it 0 Vote: I do not like it

    The hint is in the original question already. It gave an unnecessary/redundant information which could have been omitted.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

hey there i am trying to solve Day 2 P13 lost rectangle problem for almost a day now and ain't able to come up with a possible solution nor could find anything on the interent to help, coud anyone please help my with some possible idea . I would be realy helpful.

https://codeforces.com/group/yg7WhsFsAp/contest/355493/problem/P13

  • »
    »
    2 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    Hint 1
    Hint 2
    Hint 3
    • »
      »
      »
      2 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      You use one word incorrectly:

      Spoiler
      • »
        »
        »
        »
        2 months ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Oh yes, I meant the same thing just got confused with right terminology.

        Thanks for the correction.

      • »
        »
        »
        »
        2 months ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        I cant solve it... :(

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

This bootcamp will last for how many days?

  • »
    »
    2 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    2 weeks from the day of start of each section

    • »
      »
      »
      2 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      And what about topics? Only strings, arrays, math, and binary search?

      • »
        »
        »
        »
        2 months ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Yes most of them are observation based as far as what i have seen so far

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

How much time would you recommend to try to solve one problem by yourself, before moving to editorials (stuck on p48)

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

How can I get all the solution of this boot camp problems ?? I would be very helpful for me... Thank you

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I don't know if it is right to discuss it here, but it is related to a question in this bootcamp. do let me know if I am not supposed to ask or post anything here. I am new to this platform.

In a particular problem if I use.

for(size_t i=0; i * i <= n ; i++) //I get TLE where n is upto 10e12.

for(size_t i =0; i<=sqrt(n) ; i++) //The answer gets accepted

is there any difference(in performance)? if yes then an explanation will be helpful.

  • »
    »
    2 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    i * i overflows. You need to use (long long) i * i.

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

good joob errichto thanks bro for questions

»
2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

can any one help me slove primes question 1(lost rectangle)

  • »
    »
    7 weeks ago, # ^ |
    Rev. 2   Vote: I like it 0 Vote: I do not like it
    Spoiler
    Solution
»
7 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

can some one help me p22 divior count

  • »
    »
    7 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    since n is quite large, so we have to take care of the time complexity in this question.
    you can make use of this fact,
      example: 6 = 2^1 * 3^1
       total number of factors of 6 = (power of 2 +1)*(power of 3 +1) 
                                  6={1,2,3,6}
     so in this question calculate the powers of prime factors of each number and use this formula.
    you can do prime factorisation through seive it will take O(log n) operations and the loop which we you will run from 1 to n is O(n). so total time complexity will be O(n*log(n)).
    
    if you have any doubt then you can ask.
    
    and if anyone has a better approach then this then please tell me I would be greatly thankful.
    
    • »
      »
      »
      7 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      You are correct but if you implement this you will get TLE :)

      here is what I have done

      int64_t ans=0;
      for (size_t i = 1 ; i <= n ; i++)
         ans += n/i;
      

      This works it was just after 10-12 submission I realized, I didn't gave hint as it is useless here it is direct solution, Now you should think why this works.

      I have also implemented what you said but it gave TLE.

    • »
      »
      »
      6 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      THANKS MAN

  • »
    »
    6 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    Solution
  • »
    »
    6 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    why cant I see the solutions of others after day 1??

»
6 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Thanks bro.

»
6 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Needed something just like this. Thanks:)

»
6 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

some one please help in P27

»
6 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

someone help me solving [problem:P48]

»
6 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

hey can any one help me with ((p24 bubble sort))) i know what it is i get the ans but in the output format an any one help me and((( p26 selection sort)) also

  • »
    »
    6 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    Spoiler
    • »
      »
      »
      6 weeks ago, # ^ |
      Rev. 2   Vote: I like it 0 Vote: I do not like it

      tired it i think im doing it wrong can u help me with the solution

      • »
        »
        »
        »
        6 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        hmm, ill just send a snippet to at least help for this one and then you'll be able to solve p26 also.

        Spoiler
»
3 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it
  • »
    »
    3 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Corner Case : 5 1 1 1 1 1 Ranks can not be the same

»
2 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Can anybody explain me virtual contest-1 last question?

  • »
    »
    2 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    In that we just want to take the maximum frequency element greedily and add frequency*frequency to the ans(as mentioned in the question for each card), we keep on doing this till the summation of frequencies of cards!=k.

    My Submission here

    • »
      »
      »
      2 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      So first we give the characters to toastman and then calculate coin for each character by frequency in cards given to toastman

      • »
        »
        »
        »
        2 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Yes, we give the maximum frequency character to toast man first then coin calculation is done, for x characters of a type x*frequency of that character is added to the answer.