low_'s blog

By low_, history, 7 months ago, In English

Hi Codeforces,

I'm low_, currently a second year student.

As I'm taking a full-time internship right now, doing contest or training intensively for ICPC are not my top priorities anymore since I don't have as much time. On the other hand, it would be wasteful for me (maybe for the whole CP community as well, but mostly me) if I don't do anything to help maintaining my skills at this level in the meantime. So that I want to contribute, and be engaged in future contests preparations (testing problems, giving feedbacks, and maybe more) and help making contests better for our contestants. In the past, I've prepared Codeforces Round #614 (Div. 1), and helped testing Codeforces Round #616 (Div. 1), so experience should not be much of the problem for me.

The title of this blog said it all. Please, problem writers, give me a call if you need valuable feedbacks for your contest(s). I ask for absolutely nothing back :D

low_

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By low_, history, 22 months ago, In English

This is an editorial blog for HCW 19 Team Round (ICPC format). Any further question can be asked in the comments, I'll try to answer all the questions. Please, do not private message or email me, your question could be the same as others', and I really hate to answer one question multiple times. >:(

102279A - Amsopoly Simple Version

Author: low_.

Tutorial

102279B - Beggin' For A Node

Author: lantrungseo.

Tutorial

102279C - Countering Terrorists

Author: lantrungseo.

Tutorial

102279D - Dahlia The Champion

Author: low_.

Tutorial

102279E - Elevate To Dominate

Author: b21quocbao

Tutorial

102279F - Flood Season

Author: lantrungseo

Tutorial

102279G - Get Higher and Higher

Author: low_

Tutorial

102279H - Houston, Are You There?

Author: low_

Tutorial

102279I - Imitater The Potato

Author: low_.

Tutorial

Kudos to NamSPro for contributing such a complete solution.

102279J - Jumpity Digits

Author: b21quocbao.

Tutorial

102279K - Kostly Cueries

Author: low_.

Tutorial

102279L - Left or Right? How about neither?

Author: b21quocbao

Tutorial

-End of the Editorial

For further questions, again, please comment below this blog post. We will consider giving out model solution on demand :v

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By low_, history, 22 months ago, In English

Dear Codeforces community,

Lately, we have successfully organized a high-schoolers' contest: HNOI Civil War. The contest was born as a "rivalry" between two of the best Hanoi-based gifted high schools: Hanoi-Amsterdam High School and Nguyen Hue High School. 3-people organizing committee includes: Trung Lan Nguyen (lantrungseo) — as the Head Organizer, Bao Quoc Ngo (b21quocbao) — as the Head Problemsetter and coach for Nguyen Hue informatics team for this contest, and me, Dung Tuan To low_ — as the Head Coordinator and coach for Hanoi-Amsterdam team.

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By low_, history, 2 years ago, In English

Hmm, I'm thinking that not only me, but almost everyone suffers from days that he or she doesn't feel like himself/herself :/

Recently,

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By low_, history, 2 years ago, In English

Recently, I find there are many interesting interactive problems on many platforms, including Codeforces. Usually, the example testcases and generated cases are rather small and it is easy for me to type in and test it directly on the C++ IDE console. But, if the tests are as big as in 1100D - Dasha and Chess, I can't afford to spend hours typing that in (who does that anyway ==). Of course test it directly by submitting it is a solution to this problem, but what if there is a small bug in my code, how can I find it?

I find this blog rather interesting: https://codeforces.com/blog/entry/49490. It said something about the Croupier (the Interactor), which is exactly what I'm looking for. But it is implemented in Python, so there are many unknown syntax for me, and I'm unable to translate it to C++ to use. Can anyone help me out?

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By low_, history, 2 years ago, In English

There are only about 10 days left before I choke myself to death at Vietnamese OI this year.... At the moment, a part of me is really relaxed, because this year outcome won't affect my future a lot, but the other part of me is being stressful and annoying as hell, because throughout the year of 2018, I learned a lot, and obviously I cannot have the same (or even worse) than last year, right. That part of me keep pondering upon a question for the last 30 days: "What the f--- should I do to prepare for this?"

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By low_, 3 years ago, In English

I used std::map to solve 1029D - Concatenated Multiples.

I calculated that the time complexity for this algorithm which is about O(10*NlogN) for preprocessing and O(NlogN) for finding the answer, which makes the total complexity be around O(11*NlogN) (Submission: 42125423 ), which is close to the solution in the tutorial (which uses sorting + binary search).

But this code got TLE-d. I really don't know why. I used sorting and binary search to solve this afterwards and got accepted (42126892), with way less time than the std::map submission (429 ms compared with 2000+ ms).

My question is: How does std::map (or maybe even std::set) works? And why does it takes so long to process data if the procedures can be done in "logarithmic" complexity (as stated on https://en.cppreference.com/w/cpp/container/map )?

I think next time I should avoid using both std::set and std::map if possible...

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By low_, 3 years ago, In English

Recently, I've successfully promoted to become a candidate master on Codeforces, which is one of my target this year. And to celebrate this, here is my first blog on Codeforces.

Climbing ranks on Codeforces takes time (unless if you known the platform and the contests well in the first place). During that time, by pushing yourself to climb to your target ratings, you might find out that you learned a lot. E.g.: more efficient coding skills and strategies, more cohesive thinking and more creative algorithms or uses of data structures,.... That's why I always tell myself

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