Errichto's blog

[GYM] 100 Easy Problems (Bootcamp)
By Errichto, 3 years ago, In English

Target audience: newbies and pupils (rating up to 1400).
Group link: https://codeforces.me/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
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Comments Comments (35)
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3 years 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

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3 years ago, # |
  Vote: I like it +7 Vote: I do not like it

It is really usefull

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3 years 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

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    3 years 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.

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3 years ago, # |
  Vote: I like it -8 Vote: I do not like it

you mind putting some more tough questions in there .

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    3 years 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++.

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3 years 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.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

There is no problem numbered P17 in day 2

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    3 years 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.

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3 years 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.

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3 years ago, # |
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Great , it will help us a lot.

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3 years ago, # |
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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?

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    3 years ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    Sure. I don't plan to ever hide these problems.

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

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    3 years ago, # ^ |
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    Actually it says " You are not allowed to take part in the group contest "

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      3 years ago, # ^ |
        Vote: I like it +12 Vote: I do not like it

      Come on. Read the top of the blog. Or just scroll up by a few comments.

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3 years ago, # |
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Any hints/tips on how to solve P48 The line problem

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    3 years ago, # ^ |
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    The hint is in the original question already. It gave an unnecessary/redundant information which could have been omitted.

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3 years ago, # |
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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.me/group/yg7WhsFsAp/contest/355493/problem/P13

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    3 years ago, # ^ |
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    Hint 1
    Hint 2
    Hint 3
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      3 years ago, # ^ |
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      You use one word incorrectly:

      Spoiler
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3 years ago, # |
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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.

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    3 years ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

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

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

someone help me solving [problem:P48]

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3 years ago, # |
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Please help in p54 https://codeforces.me/group/yg7WhsFsAp/contest/355504/problem/P54. Why XOR works??

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    3 years ago, # ^ |
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    XOR of two equal numbers is 0. So also XOR of any even number of equal numbers is 0.

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3 years ago, # |
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Since someone necro'd this, I request 100 hard problems bootcamp!

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2 years ago, # |
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Great

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20 months ago, # |
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Hello, I am trying to solve the Lost Rectangle problem. In my first try, I used normal way to find out the factors which led me to failure because of time limit.

Later I tried to implement sieve for prime factors, and again I got stuck for the 7th test with the input 1000000000000. I took integer which will not support this long. But when I tried to use long long I started getting memeroy stack issues. Also, I am facing the array size limit here as well.

Here is my last submission code: https://github.com/ahsanaasim/problem-solving/blob/main/codeforces/355493/P13-Lost%20rectangle/main.cpp

Is my approach entirely wrong? Or is there a way to solve it the way I am trying

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6 months ago, # |
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Helpful, thanks.

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5 months ago, # |
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Hi, can anyone give me hint on problem P44 (math day5)

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    5 months ago, # ^ |
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    It is a simple combinatorics problem, think like this how many max dashes can you have?

    Then use if we have $$$m$$$ like objects and $$$n$$$ like objects then number of ways of arranging them is simply $$$\frac{(n+m)!}{n! m!}$$$

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      5 months ago, # ^ |
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      thanks, it is the firsr time for me to solve combinatorics problem.

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2 months ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

Hello there!

I know this post is 3-years long, but I think I found an issue that is worth noting.

Alert: This comment contains spoilers on problem P19 — Mountain peaks.

This code here uses binary search to find the minimum divisor d of n that could be the number of peaks which are visited every day and prints n / d. However, using binary search is not correct since the function here is not monotone, although the submission received an AC verdict.

Here is a test which would make the code fail:

70

1 2 1 1 1 1 2 1 1 1 1 1 1 1 2 1 1 1 2 1 1 2 1 1 1 1 1 1 2 1 1 1 1 2 1 1 2 1 1 1 1 2 1 1 1 1 1 1 1 2 1 1 1 2 1 1 2 1 1 1 1 1 1 2 1 1 1 1 2 1

Also, some other implementations of binary search such as this one passes the previous test but would probably fail on this one:

35

1 2 1 1 1 1 2 1 1 1 1 1 1 1 2 1 1 1 2 1 1 2 1 1 1 1 1 1 2 1 1 1 1 2 1

I hope this matter would be considered.

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