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Hi, the three top two won the championship with the outstanding performance of AK! Question D (and Question H), the person who made the question + the preparation of the question surface, come to report. Ah, I haven’t had lunch yet… I went to dinner after I finished writing the QaQH question. Someone actually passed the question for 10 seconds… But it is quite happy to see that everyone has passed this question, so let’s take it as a warmth for everyone. At the beginning of question A, everyone was reckless and greedy, so we didn’t care too much. After two hours, no one had done this question. We tested a code from Peking University and found that it was actually passed… Then we found that Special Judge wrote a fake, and the pot was fixed with the hand of an elderly single dog (then I found that the Special Judge used in the test of Peking University was also fake. They wrote that they were also fake greedy……) Then exactly three tops came to hand in the first shot and then T, and then we started to retest and saw three tops. Two ACs were issued for the second time. After the retest, it was found that only three of the previous submissions were ACs… We apologize if it affects your experience of doing the questions. In the end, there are only two AC teams in this question, so it can be regarded as a more serious question on the rankings. In fact, this question is not too difficult to repent of greed, just use the heap to maintain it. Question G is another question that has been crooked. When testing the questions, we always thought that this was the easiest question in the audience except for H, but it was abruptly turned into a gold medal question… When I wrote the question, I tried my best to remind everyone that there was a pit on February 29. ……L question is a question that the question group thinks it is difficult but the contestants cut it out one after another. It was only after seeing the actions of the players that we realized that we wanted to be complicated…Anyway, everyone is still very good. The T_TI question is to see which students ran after seeing computational geometry. Question J is the data I created and written. I don’t know why everyone doesn’t seem to understand the meaning of pairwise distinct… In short, this question is quite interesting, it is a test of your observation ability. Question M is a fairly satisfactory data structure question. After observing the nature, it is enough to go to the chairperson tree, and the number of people who passed it is relatively large. The K question is a lightweight mahjong question (the amount of code in the mahjong question is relatively small), and the number of people who passed it exceeded expectations. Question C is a more conventional DP question. I don’t know why there are fewer people who have passed it. Question D is a question for the investigators to boldly guess the conclusion…Of course, the detailed proof of this question is also quite interesting (I wrote a long paragraph), if you are interested, you can think about it. Question F is a more routine palindrome automata question. Maybe the backtracking operation is not widely known? Question B is a better cost flow question (although it looks very slick, but it does have a more clever second point). It seems that everyone has not prepared a board for the upper and lower bounds… It seems that there are only three top two for E question. /jk Is it a relatively new question? Regarding the problem that the title book does not have a cover and the order of the title book is inconsistent with that of Niuke, I apologize to everyone. Since I repaired the problem surface pot again last night, the problem booklet was generated very late, our classmate who was responsible for adding the cover disappeared, and I didn’t know how to stitch PDFs, so I did it like this. The order of the questions is in the lexicographical order of the question names, but I changed the name after one question, and I didn’t find it. I once again apologize to the contestants and volunteers, and hope you can understand… Finally, I would like to thank the organizer, organizer, and volunteers, thank the students in the question group and the proposition group, and thank all the contestants for their strong support! I hope ICPC can do better and better!


By zhiwo

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7 months ago

I’m not sure about the specific situation, but I think that in the foreseeable future, especially for these online competitions, a big expansion is inevitable. As for whether this time a bunch of places have been suddenly released, the number has suddenly increased to 800. I don’t care much about the super division. Secondly, if there are more teams, it doesn’t mean you can mix as you should. In the case of big competitions everywhere, if the cards are still issued at 10%, 20%, 30%, then everyone don’t play, just get the cards back. Home. Under the new environment, to ensure that the gold content takes into account the actual situation, only the upper limit of the brand can be restricted. If you have to have the entire rules correct and procedural justice, you do not recognize this matter and require the so-called fairness and justice, welcome to register for this year’s Macau competition. Again, I don’t care whether the organizers will change the rules day by day this year, hiding the rules and muddy mud.

7 months ago

It’s time to write a small essay again. This time I feel that there is no good comment on the topic. My teammates basically read one question every time. The highlight during the game may be that teammates prefer to turn off devcpp immediately after editing. Here is the focus of being invited to narrate the actions of a certain teammate A in the last two hours from the perspective of an onlooker. B: There are still two hours. I can’t finish writing the three inscriptions. I: It should be okay. Mahjong is pretty fast, 5^9 is as small as 5^9. I can already fully understand it. jpgA: (pointing to the palindrome tree border board) You give me these two lines and I can write anything else. (Shortly after) Me: How can there be fourteen ten-thousand-draw cards on the grass? B, you go first. (Ten minutes later) B: It’s gone. A: I have fully met. B: It’s off work now. (Shortly after) Me: Sample RE, as expected. A: Here comes, it will be over. jpg (in one minute) I: I understand, here, here, here, here and here, just change it. A, B: How has the grass been used? How is the grass real? Passed (not long after) A: Let me test a sample. Me: Why are the answers to the questions behind the first set of data all the same? Think about it. B: Is it cleared? A (stared for a while to clear): How could it be cleared? Isn’t it cleared? (Changed) This doesn’t seem to affect it. B, me: this, this and this place, do you want to add a clear try (1000 years later) B: big brother, hurry up, brother, it’s going to be closed (a long, long, long time later) me: you clear the entire array Have a try? A: Why did you really pass it? Is this reasonable?. jpgB (I changed it back and forth a few times and I haven’t found any errors): Fast delivery, fast delivery, the list is closed, A, you have to be responsible. A: …A: (Longmen swearing) How come this character is thrown in without subtracting a. A: After that, will anyone come to play chess? Let me write an API how to play Go. Will anyone come to play JiuRui? B: OK, OK, let’s play chess, and you will be in charge of counting the stones. I:? Jiulu is too small. Me: I also want to play with you (Maomao Cry.jpg) and then I saw the passionate ICU bloody battle between two netizens A and B. The situation on the field was reversed several times. Dead chess can also live. Frankly speaking, this is the first time I have seen the ups and downs of Jiulu Chess. I would like to ask how to evaluate the ICPC 2020 (held in 2021) Kunming Division? I feel that the quality of the questions is a bit average compared to the past. Thanks to avoiding the reverse cross when selecting the competition area, such a dirty submission can’t be played against them in this kind of field. jpg In addition, the flower cake is quite delicious, there is There is no organizer channel to buy the green channel (fog) at a low price. Finally, I hope that all the awesome teams who have not come to compete on the same stage will show mercy to ECF.

7 months ago

Ah, the student who wrote the question did not write the solution to the K question. Let the person who wrote the K question write the meaning of the question: Yui Yagi has a set of mahjong tiles, ask which tiles can stand upright, and declare every possible upright card. Output the card type of the draw. (Does not consider Guo Shi Wushuang, the special rules of seven equals, only consider the most basic 4*3+2 card type) There is a “Mahjong” sample question on page 21-25 of “Algorithm Competition Introduction Classic-Training Guide”. This question is Determine whether a set of 13 mahjong tiles is drawn. The method given by Mr. Liu Rujia is to enumerate “incoming cards” and use the DFS method to judge whether the cards are tied. So naturally this question has a very simple idea: enumerate “rejecting Zhang”, then enumerate “incoming Zhang”, and then violently search according to the method in the book, and the result can be obtained. The complexity is 34*14* (the complexity of a DFS). But in fact, the amount of data is very large. Direct search like this may result in TLE (someone can write AC in this way, but some people fail to write), but it may involve some faster writing of constants, or some pruning What, can pass this question. However, the actual practice of the question maker is this: Consider the 13-card draw type. After separating straight, engraved, and sparrow heads, the missing card may have such a situation: two-sided listening: That is, the front/back of a set of straights (or only one side, which is called “side card” in some places). So only enumerate the “rounds”. For the remaining 13 cards, we Try to draw a straight or a pair of trump cards (bird head), then there will be 2 or 1 cards left in the end. If there is one left, it means that this is a single fishing, and only listen to this one. If there are two remaining cards, according to the relative relationship of the two cards, judge whether it is a double-handed, a bumper, or a double-touch (double-touch here is only used to listen to the remaining pair, because you enumerate the head of the bird At that time, both pairs will be enumerated and both will be searched). In this way, the complexity of a search is roughly the same as the original judgment of whether it matches the complexity of the card, but the number of times you search is much less, so you can pass this question. Summary: Although there are some minor mistakes (such as a spj that caused WA’s data to be AC ​​at the beginning of the A question, and this is not a problem with the question group of our school), the order of the questions and the lack of a cover are Some deviations occurred during the handover with the members of the test group. After we realized the problem, we also issued an announcement in time. In short, the quality of the questions in this game is still acceptable, at least the part of the question group in our school is very reasonable, and there is no big problem. PS: Not all topics are published by our school. Acknowledgement: Thank you to the leaders of ICPC Nanchang in 2019 for their guidance. They have gained a lot of experience for this proposition work. Thanks to all the students in the question group + test group for their hard work, thanks to the platform of Niuke.com Support, thank you contestants for your participation and forgiveness! Everyone has worked hard!

7 months ago

First of all, congratulations on the successful hosting of Kunming. After all, it is also an inexperienced organizer. He joined the coaching group after the first version of the plan. From a small competition area of ​​80 teams to a large competition area of ​​800 teams, it is indeed a lot of twists and turns, very difficult, and I am very grateful to Kunming. The organizer can listen to the opinions of all parties and revise the plan repeatedly. The flower cake and the sweet-scented osmanthus chestnut cake are still delicious. But let me mention the problems that I felt during the process of being a volunteer. Warm-up match: 1. The identity verification was verified for at least two hours, and in the end it was not all verified. Only one team in our school was tested before the game, one team was tested in the game, and the remaining two teams did not perform identity verification until the end (too late or forgot?). And the method of identity verification is different from the official game. 2. A group of friends wanted to simulate the process of going to the toilet in the warm-up match, and was told that this part of the warm-up match was not provided. The warm-up match should require volunteers and players to familiarize themselves with the race process. No one actually warms up to write questions. 3. Before the warm-up match, the method of screen recording and submission was not emphasized. After the players handed in the paper, the reply I got was “I will open a questionnaire later”, and later said “The warm-up game recording screen cannot be turned in” later. 4. The grouping is very chaotic. There is a general group, a general group of examination rooms, and a group of volunteers in the examination room. Some things can obviously be said in the general group (or should be said in the general group) in the examination room that includes the contestants, and put in the volunteer group, so that the volunteers have to notify the players. Two group messages are also easy to cross each other. Official competition: 1. Test question printing question (that is, the 10s question that everyone likes to hear). The notification message is very inconsistent. Candidates can print out the test five minutes before the test, but only two minutes before the test can the test taker get the question. I asked a question in the small group, and the response I got was that it could only be printed by volunteers. 2. The problem book cauldron. The question book has no cover (unexpected), and the question number does not correspond to the one on the Niuke website. Almost 40 minutes after the start of the game, I told me to reprint the question book after giving feedback on the order of the question book. Obviously, the things that can be solved in the announcement of the Niu Ke must be re-tested and sent to the players, that is, the printed materials are delivered during the game. I believe that everyone understands the loopholes. 3. The rules are uncertain. Printing test questions is also one aspect. I listened to many different answers before and after. There was also Tencent Meeting 3 where the team members went to the bathroom and entered the examination room. It turned out that Tencent Meeting 3 did not open at all (a conflict with another Tencent meeting). Finally, QQ video was used. Originally only needed to line up the school team, now it has become a test room team (only one person can go at the same time). Originally, the toilet environment was required to be photographed only to follow the door (although it is really embarrassing to go in and shoot). Let’s talk about other thoughts. Zhankeng blesses the third team of our school

7 months ago

Regarding the accuracy of question I, I will issue AC this question once on the field, and the eps is 1e-8. Find the intersection of a straight line and a line segment, that is, after finding the intersection of a straight line, judge whether the intersection is on the line segment, and when judging the point on the line segment, it is better to omit the step of judging that the vector is parallel, and directly judge whether the point is between the two ends of the line segment. For the reason, the first intersection point itself falls on the line where the line segment is located, so the step of judging that the vector is parallel is unnecessary. Secondly, finding the point of intersection itself is an operation that loses accuracy, and if the accuracy is not relaxed when the parallel is judged, there is a high probability that the error will explode. This accuracy problem should not be a data problem. Some other geometric problems can’t be passed without paying attention to this detail, such as Airport Construction of WF2017. upd: The problem I mentioned above for using the kuangbin board is the problem of this function. The conditions in the red circle in this question are best removed, otherwise unnecessary accuracy problems will occur.

7 months ago

As the 19th Xuzhou rank6 original team, no one noticed that M was the original question during the game. Forget the topic after training, no progress. So in Kunming, he also played rank6. During the competition, copy the board that handed in the red book (after copying the straight line to find the line segment, and then copy the point to see whether it is on the line segment, the accuracy of the two boards are qualified, but the accuracy is not good for stringing) I question wa It’s been a long time. Finally, I carefully read what was written on the board, and removed the sand crane (unnecessary) eps. (Considering that two numbers are both integers within the range of double’s max safe integer, double stores its exact representation, and the sign of its product is directly derived from the sign bit of the two numbers, so there will be no error problem.) The magic is said eps can be too big…

7 months ago

The retirement game was very tragic. The warm-up game went to the evening class to ask for leave, and the Dushu Lake teammates did not come. The last game was really too long without training, and I couldn’t keep up with my thinking. We have been stuck with the L-question all the time, but we have been stuck in the mentality and collapsed. The question of swapping the order is a simple thinking because the brain was completely blank when I wasted too long before on L. When I went up to type calculation geometry, I even wondered why the range of k can reach 1e6? The maximum tmd is not 1e3. Is it because my thinking is wrong or the question is read wrong? After the end, the team next door cgg told me that if he shows 1e6, you can directly output -1. I am stupid. What were you doing during the game. The state of the whole team is like this. The only interesting point is that the next team xygg said “Mahjong? Mali sauce!” during the game. Then I thought that my girlfriend is a pure Sichuanese. If she was there, I should be able to get started quickly. But I also thought that Sichuan Mahjong seems to have nothing in the north and south. These cards hh from my previous lucky player who got the bronze medal. , Maybe I’m too weak, Kunming’s list has been taken crooked? I feel that after signing in, it is reasonable to exchange the order of questions and then reverse the order and calculate the order of geometry? 2019.6.2 icpc Nanchang 2019.11.2 icpc Xuzhou 2020.12.20 icpc Nanjing 2021.4.3 icpc Kunming bronze medal retired, I was still an ordinary computer student in the end, icpc gave me the opportunity to be abused by the top algorithm competitions in the country , Also saw the gap, thank you very much!

7 months ago

A magical coincidence: The team that first passed the question I in this field was a lucky winner from Beihang University, who ate mian at night; the team, I guessed it blindly because the name was very similar and I opened this question. It turned out that it was actually very simple. Then smoothly brought the crooked list back to the 233 topic background: it was originally a high-speed rail journey in Miss, but it was changed to Mr. Main in order to avoid suspicion. City S and City T are Wuhan and Beijing. Sitting on the high-speed rail and seeing the big windmill outside the window, I thought about it by the way. The first version of the problem hoped that the positive solution was probably polar angle sorting preprocessing + line segment tree query. Later, after thinking of various methods, the most obvious n^2 violence was not stuck, so it compromised and it became a big water problem…About @陈靖邦I don’t know if the accuracy of the feedback is a common situation. It’s no problem if the error is set to 1e-5 in the previous test. I will check it again. Before the game, we also asked multiple people to test the problem. During the competition, no players were asked to ask questions about accuracy. I researched the amount of questions after the competition, and I felt that it was quite in line with expectations. In short, I hope you all have fun! Thank you for your support and forgiveness from the coaching team, the volunteer team of the test team, and all the contestants!

7 months ago

This old salted fish player should also write about the experience of today’s pit teammates… At the beginning of the game, to print the title, an old printer used did not even have a paper output slot. You need to take the printed paper with your hand. So I wanted to look at the printed question while holding the paper that was coming out with my other hand. As a result, the printer ate the paper it spit out. T_T looked at the question backwards, and found that M turned out to be the original question, 2015 I saw it during the training camp of the Shandong Provincial Team in 2016. Seeing all the upstairs saying that this is the original question of 2019 Xuzhou, I can’t help but sigh that I am really old when I wrote M in QAQ, and found that I almost forgot what the chairman tree wrote. Fortunately, I adjusted it to 1A. After M, my teammate gave me an I and said that this is an XX question, but no one can write computational geometry, so this question is left to you! Okay, don’t panic. Fortunately, a few minutes before the game, I cloned a well-known 1k+ star template KACTL on GitHub. It shouldn’t be a big problem. I wrote the sample quickly and handed in a post, WA. Teammate: Eh, how did you directly judge this board == 0? Woc quickly changed to use eps to judge 0, and WA made another shot. Teammate: Why do you want to return this formula here on this board? can not read it. Then just return 0 directly, change it, and then WA sends it again. Fall into despair. . . Began to doubt life. Is it too much precision to output 10 digits after the decimal point? Try it with 7 digits. Another WA shot. Is it because my sample will output -0, and then the spj will fail? Special sentence -0 Try it. Another WA shot. Is the precision of double not enough? Try to change to long double. Another WA shot. Is the accuracy error of the method on the line segment of the current judgment point too large? It seems that the accuracy will be much better if it is changed to use the argument to judge. Another WA shot. Is there a problem with this fabs’ support for long double? Try to change it to handwritten. Is the eps set badly? Try it out. Another WA shot. Teammate: You made a mistake in the argument, it should be <eps or> 2pi-eps! Woc made sense, changed and changed, and WA made another shot. With half an hour left, the mentality completely collapsed. Start looking at other questions. After watching B, loudly said: This B is just a naked fee stream! (Laughter from the team next door) Teammate: Then tell me how to build a map? Me: I think about it. After a few minutes, I realized that I really didn’t know how to build QAQ for B, so I started to look at D. How is this D? Q and n and k are so big, it should be a conclusion question. Let me just guess the conclusion that “human beings win if and only if”, at least it can pass the example! I grabbed the computer and handed in a post, WA. A few minutes later, the teammates said, let’s change the conclusion and guess, “Humanity wins if and only if”, and wrote a quick multiplication + fast power, and it turned out to be T? woc That shows that the conclusion is correct! Quickly change to use __int128 for multiplication, A is now A! Another teammate was helping me adjust I, and even tried out a set of examples at the end of fifteen minutes! Meow, it turned out that when I judged whether a point is on a line segment, I only considered the angle of this point relative to one end of the line segment, and forgot to consider the other end point. This is the story of the old salted fish player who overturned his teammate. After the T_T game, he looked at KACTL and found that OnSegment (a function to determine whether a point is on a line segment) clearly says: Use (segDist(s,e) ,p)<=epsilon) instead when using Point<double>. So I found the first version of the code, replaced OnSegment with segDist, and found that it was AC happily (covering the face)

7 months ago

This season is really very, very regrettable. All the xcpc competitions that our team participated in have played silver medals. It can only be said that luck and strength are slightly inferior. Although the Kunming station was the most painful one, it was also the closest to the gold medal. After signing the H and L in the early period, the three people have been stuck in the third line until autistic. I saw that the I question was a simple question of finding a straight line and went directly on the machine and then inexplicably wa, the teammate went to the chairman tree, and there was also a simulation. It wasn’t until more than two hours that the simulated bug was found that the card type enumerated type 7 became 6, and then the dp of G on the teammate was always wa. The early rhythm completely collapsed. After more than three hours, we all felt that we had no choice but to win by the number of questions. The fake algorithm also had to be rushed but it was completely awkward. It wasn’t until three hours and fifty-five minutes that I changed the eps from 1e-7 to 1e-5, and then I lost question I inexplicably, and my teammate also found a bug and changed the transfer of question G through clarification. At this time, we dared to look at the next list and discovered that G has only passed a dozen people. Although there are only forty minutes left, as long as we pass both M and J, we can still get gold. So I immediately went to J with a teammate, and the teammate who wrote the chairman tree tried to optimize the constant. I quickly discovered with my teammates that J’s odd and even rings can be completely split into a pile of 2-membered rings with one swap, and then the swap will be sorted in one round. The teammate with the strongest code power hits J on the machine, but because I don’t understand the chairman tree at all, I don’t know how to optimize or how my teammates write, so I can only try to comfort his teammates and trick him into rushing past. Ten minutes is basically the two sides take turns on the machine-print errors-and then on the machine… the mentality is very depressed. In the last five minutes, we wrote the J code correctly and handed in the optimized chairman tree. But the J question is wa soon, we dare not look at the result of the chairman tree’s submission and immediately come back to think about the bug of J, but in any case, we can’t think of where wa is. All the hand-made data in the self-test are correct and can only be changed. And just hand in a code before the end. After the game, we were desperate to see the final list: the chairman tree ac, but J’s dismantling was wa, and six questions were at the bottom. After the game, we submitted the code of J and found that the pass rate was 67%. We felt something was wrong, so we changed the value of the output to the subscript of the value and it turned out to be ac? Recalling that half an hour ago when my teammates asked me to confirm the output method, I directly judged the output value based on the values ​​of x1…yk are pairwise distinct above, but I didn’t see pxi in the following text. Pyi explained xi and yi was the next. Mark! ! ! After all, we lost to time and ourselves. The difference of a few letters caused us to lose the gold medal. Although after the game I also thought that it is not easy to turn out three questions in the last hour, and it is a bit idiotic to turn from iron to gold for another question, but this clumsy eye is really a too low-level mistake. Recalling ccpc Weihai, we were unable to recover because of the time penalty for the grouping of backpacks; icpc Shanghai finally rushed over because of the missing category discussion in question D, which resulted in no time to write the L that was the correct conclusion; this was a complete explosion in the first and mid-term Kunming. In the end, it was indeed only a few letters away from the gold medal. Maybe we have made some progress, but we only have three silver medals left. I’m very sorry for my teammates and myself for more than two years of hard work, and I don’t know if there is a chance to continue playing next season and get the gold medal with my teammates. In short, I hope ecfinal, which is likely to retired, will not leave regrets.

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