## NOIP 2018 travels

Change, this is my summary of this year's NOIP, from the site selection of the Tianjin competition area to the new campus, and to CCF update the "master machine" which has been criticized for countless times by the numerous players, it can be seen that NOIP's continuous improvement and the degree of attention are constantly improving. Talk nonsense. Let's talk about the idea of this examination.

## Day 1

The first question is paved the road, a simple greedy, casually playing a tree array 30min A to cut the next question (actually time is longer than 30 minutes).

I saw second questions, math and math questions. However, a simple analysis can show that if a number can be expressed by other numbers, then this number is useless. Otherwise, it must be useful (obviously). The hand played several sets of samples, and found that the thought was correct, and then played a sieve, 1H A finished and cut a problem. There is a hole in the sieve. Like Euler sieve, a mark must be made, otherwise the complexity will not guarantee that it will be properly T.

Then go to the bathroom. Take a breath of fresh air. Maybe 2.5h has passed.

Look at the third question. After reading two times, I found that it was a tree like dynamic programming. Unfortunately, my tree dynamic programming was learned last week, knocking out violence, writing a pair of shots, and getting several sets of test data to test and hand over.

The topic of Day 1 this year is that it has all been hit by the Internet, but unfortunately I haven't done it yet (ZG Dalao two months A dropped 300 topics%%%).

## Day 2

After reading the question, it is found that the data of the first question is particularly magical. It is a single loop tree. It considers the upper part of the broken ring and then enumerates it. The complexity is O (n^2), but it also requires the minimum. So the idea in the examination room is to arrange the sequence again, O (n^2logn), taking into account this year's CCF. There are not many things that are changed because of the sort of every time. Luckily, I finally asked for my "excellent" card skills. Specifically, using vector to save edges is T.

The second question is "Cao", which is also a mathematical problem. However, because of its high heart, it has made a mistake in the examination. It must be hard to resist. It turned out that if I hadn't had a big fortune, T3 would have been adjusted in the last 30 minutes, otherwise it would be cool, and it would cost me 1. For an hour, but finally decided to change the topic and reduce the loss. When the last question came out, I came back to find several sets of idiot data. My hand knocked on a watch and handed it up. Finally, I only deducted 5 points on the basis of the violence. Thank CCF for the weak data.

Third question, this is NOI Plus. No, a violent fight was made.

## summary

Generally speaking, experience is OK, but the mistakes made before, this time, the time planning is really, very, very important.

In addition, I feel that this game itself is very bad, because I always insist on the principle of code readability, resulting in my code generally more than 2 times longer than others, this may be changed, after all, playing a competitive game, rather than long-term maintenance of the project.

394, I have been very satisfied with the achievement of nearly 400 points.

NOI 2019, we'll see you next year!

The picture is NOIP 2018 Tianjin examination hall, Tianjin University Beiyang garden campus.