hxu10's blog

By hxu10, history, 4 weeks ago, In English

Currently I have already got a PhD in physics, but I would like to find a job in computer science (like data scientist or SDE) instead of postdoc. However, my disadvantage is that I have no internship and programs to write. (My school forbid us to take internship that are not relevant to our study)

My advantage is that I have some "good" competitive programming results, like entering 2022 Google Code Jam round 3, Google Kick Start top 100 for three times.

I would like to include my codeforces rating in my CV, but many friends of me said to me:"no recruiter know codeforces." So I would like to ask everyone, does anyone has ever included codeforces in CV and what consequences?

Another question is that, if you write codeforces(or actcoder, leetcode...) results in CV, what rating do you write, like maximum rating or current rating? Thank you.

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By hxu10, history, 3 months ago, In English

I have participated in four div 1 only contests, and every time ends up in very big negative data. First time, I thought it is just coincidence, but 4 times, every time I lost big, then in the contest 796 , I do an experiment.

The score distribution: div1: 500, 750, 1500, 1500, 2000, 3000 div2: 500, 750, 1250, 1500, 2000, 3000

ABC in div1 corresponds to DEF in div2. According to each problems accepted users, the difficulty ranking of each problem is div2A <= div2B << div1A < div2C < div1B << div1C << div1D..... More difficult a problem is, more time a user expect to spend.

Assume a user takes part in div 2 contest and solve 5 problems, and finish each problems in time 0:05, 0:10, 0:40, 1:00, 1:50, with no wrong submissions. His score, according to the rule should be 490+720+1050+1140+1120 = 4520, he will rank 93 in this contest, and his performance rating is 2147 according to the rating predictor.

Then, this user takes part in div 1 contest, since div1C is very hard, and he is not able to solve it. He will solve only two problems, with time 0:20, 1:10 (each subtract 40 minutes), and his score will be 460+540=1000, and his ranking is over 550, with performance rating less than 1900.

That means, if his current rating is 1899 and participate div2, he will gain big rating (about +60), however, if his rating is 1900 and participates div 1, he will lose rating and go back to expert.

I would like to ask if you all have the same feeling, that is, it is harder to gain rating in div1 only contest?

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By hxu10, history, 3 months ago, In English

Currently this contest will start in less than 20 minutes, and I find no blog about this contest, so I decide to write one. Here is the link:
Code Jam 2022 Round 2 link

Last year I ranked 1672 and failed to qualify for round 3, this year, I feel that I improve so much, hope I can get a T-shirt. Good luck everybody, and any discussion is welcomed.

(updated: Finally I ranked 484 and won a T-shirt, so excited, see you in round 3! )

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By hxu10, history, 6 months ago, In English

I know it is not very appropriate to discuss politics in this CP platform. But this war is too big, and has already influenced this platform. The go study round has already been postponed because of this.

In many social media platforms, there are many jokes about the war, like taking Ukraine women home .... I cannot be more disgusted seeing these comments. War is war, no matter what excuse, it will hurt people badly. It's not game, it's real. I stand against every joke about this war, and hope the war end as soon as possible.

I post this because many people in Ukraine start hating Chinese after seeing these jokes, and ministry of foreign affair suggests Chinese in Ukraine to not expose their nationality in pubic to protect themselves. I would like to say this cannot represent all Chinese. If you see a Chinese on the street, don't assume they support Putin. China already had so many wars and has been invaded by so many countries, Japan, US... we love peace. I stand against every war.

Finally, I send my best wish to Ukrainian, please be safe, and may the war end quickly and back to normal as soon as possible. I also send my best wish to Russians. Standing with Ukrainians does not mean standing against Russians, they are both victims of war.

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By hxu10, history, 6 months ago, In English

I have participated over 60 contests. I became expert in my 12th contest and reach the rating 1800 at 17th. I feel very confident and my goal then is master and grandmaster.

However, I find it extremely difficult to move further. I have stayed between 1747 and 1965 in the nearly 30 contests, every time I reach 1900, my next contest will more likely to have negative rating and make me drop into expert again. My title keeps expert -> candidate master -> expert -> candidate master -> expert ....

I would like to know if any people have the same feeling as me, like very hard to reach purple or very hard to stay purple. I heard from another saying: "hard work makes you expert, but if you want master, you need talent. " I don't know if the saying is true.

----- UPD: Sorry for the title change. The gap between expert and candidate master is actually only 1. I previously want to ask if a stable expert is very hard to become a stable candidate master. Reaching candidate master by chance and drop to expert next time does not count for stable candidate master.

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By hxu10, history, 7 months ago, In English

The codeforces round #765 is over, among the top 10 rated users, 5 are newbies, 2 are specialist. Ranking are as below. rankings

If you click on these newbie users, like the 3rd place @Alan_boyfriend, you can see the user previously take part in round 764 and rank 1st. The 8th place, @Asaoix, participated in round 763 and get 6th. And so on....

These newbies, I called, are fake newbies. Because they are not newbie level, they are far more than that. Some of the newbie users are even red level, they have low rating only because they are new users and only take a few contest, and the rating cannot accurately measure their level.

Besides, you will not get your performance rating in the contest, if you get rank 1, your new rating will not be rank 1 rating, you new rank will based on your previous rating and this contest performance. If you have 1400 rating, and your performance is 2600 in a contest, you will get probably one third of the difference, say 1800. But if you are 2600 level, 1800 can still not measure your real ability. In general, you need to take at least 4 contests to have your rating consistent with your ability.

Why I mention this ? I am not making complaints. It's a good thing, since codeforces has been expanding from time to time, more and more talented programmers are joining in codeforces platform. They have already achieved well in other platforms, and codeforces should welcome them. The only thing I care is the rating calculation.

In each contest, you get rating based on how many users you defeat, and how many users defeat you, and what their ratings are. If you defeat a user that have high rating, your rating will increase, and if you are defeated by a low rating user, your rating will drop. The detailed rating calculation are listed here

Therefore, if you are defeated by these fake newbies, the rating system will say: "Hey, you are so suck. You are defeated by these newbies, your rating will not be good." Which is not true. You cannot make them unrated, it's unfair to them. And here is my suggestion, like div3 does:

Make a pool of trusted users for all contests(not only div3). Every rated users who participate more than 3 or 4 contests will be marked as trusted users. Everyone's rating will only be determined by these trusted users, and every users within the rating range will be rated whether it is trusted or not.

Another reason that so many fake newbies is that they are the alternative account of some high level user. It is discouraged, but it is very difficult to discover. Since many users, they have multiple accounts, and only use one account in the contest. By expanding the "trusted users" idea, they will have no influence to the low level users.

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