### Errichto's blog

By Errichto, 14 months ago,

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

• +251

| Write comment?
 » 14 months ago, # |   +19 Thanks a lot :D I'll try to solve all of them in the upcoming days
 » 14 months ago, # |   +7 It is really usefull
 » 14 months ago, # | ← Rev. 2 →   +1 Can those not in the rating range specified above not submit ? Edit : Just checked, they can
•  » » 14 months ago, # ^ |   +25 You are allowed, but the problems should be easy and boring for you.
 » 14 months ago, # |   -8 you mind putting some more tough questions in there .
•  » » 14 months ago, # ^ |   +11 These are problems from a camp two years ago. The participants were beginners just after learning basic C++.
•  » » » 12 months ago, # ^ |   0 can user or python also solve it because you mentioned C++. Btw I have solved some them already and its in my favourite.
 » 14 months ago, # |   -28 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.
 » 14 months ago, # |   0 There is no problem numbered P17 in day 2
•  » » 14 months ago, # ^ | ← Rev. 2 →   +16 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.
 » 14 months ago, # |   +14 Reminds me of whenever I say I should start over competitive programming from the beginning since I am not good at the basics.
 » 14 months ago, # |   0 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?
•  » » 14 months ago, # ^ |   +12 Sure. I don't plan to ever hide these problems.
 » 14 months ago, # |   0 When I try to register it says "you are not allowed to enter", I am new to this platform. how to register for this.
•  » » 14 months ago, # ^ |   0 Actually it says " You are not allowed to take part in the group contest "
•  » » » 14 months ago, # ^ |   +12 Come on. Read the top of the blog. Or just scroll up by a few comments.
 » 14 months ago, # |   0 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
•  » » 14 months ago, # ^ |   0 Hint 1Prime is a big hint in itself. Hint 2The Area A is made by two integer (as given) sides. So, using this fact you can determine that for any integer to be the height or breadth of rectangle, It should evenly divide the A. Hint 3Just find all the prime factors of A, and then say for any factor p, we can treat it as 1 of the side of rectangle. Therefore, the other side is A/p. Now, you have both the side. Find the Perimeter using the same idea for all the factors of A, and print minimum one to the result.
•  » » » 14 months ago, # ^ |   0 You use one word incorrectly: Spoiler"prime" -> "divisor"If the area is 100, possible shorter side lengths are 1, 2, 4, 5, 10. These are divisors, not primes.
 » 14 months ago, # |   0 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.
•  » » 14 months ago, # ^ |   +11 i * i overflows. You need to use (long long) i * i.
 » 14 months ago, # |   +1 someone help me solving [problem:P48]
 » 12 months ago, # |   0 Help in Problem P05 of day1 !
•  » » 12 months ago, # ^ |   0 Solution#include using namespace std; int main() { string s; cin >> s; for(int i = 0; i <= (int) s.length() - 7; i++) { int counter = 0; for(int j = i; j < i + 7; j++) { if(s[i] == s[j]) counter++; } if(counter == 7) { cout << "YES\n"; return 0; } } cout << "NO\n"; } 
•  » » » 12 months ago, # ^ |   0 Would you explain please !, why s.length() -7 ?
•  » » » » 12 months ago, # ^ |   0 Errichto did a video on this exact topic 2 weeks ago. Link below starts at (4:35) but watch the whole video:
•  » » » » » 12 months ago, # ^ |   0 Thank you bro !
 » 12 months ago, # | ← Rev. 3 →   0 Your code here... 
 » 12 months ago, # |   0 Would you still recommend this if we've already completed the A2OJ ladder rated for <=1300?
 » 12 months ago, # |   0 Help with problem P06 — Helpful Maths ! ,Day 1.
 » 12 months ago, # |   0 Erricto! Why are you showing the people and me exclusive,these problems why are you making them lazy motivate them for solving hard problem tell them how you struggled at reaching this level.
 » 12 months ago, # |   0 Thanks..