This article relies on ChatGPT-4 for translation.

China has been hosting the National Olympiad in Informatics (NOI) since 1984. Over the past forty years, it has developed a unique system. I intend to provide a brief introduction to this system for everyone.

In mainland China, about 100,000 people prepare for informatics competitions each year. The first step in these competitions is to participate in the CCF Certified Software Professional Junior/Senior (CSP-J/S). CSP-J is for contestants aged 8-14, while CSP-S is for contestants aged 10-18.

CSP-J/S is divided into two stages. The first stage tests general and practical computer science knowledge, such as base conversion, principles of linked lists, and reading programs to answer questions. About 40,000 to 50,000 people pass the first stage of CSP-J/S. The second stage of CSP-J/S focuses on programming. The CSP-J second stage exam lasts 3.5 hours, while the CSP-S second stage exam lasts 4 hours, each with 4 problems. Approximately 20% of the contestants in each province can receive a first prize.

The second step is to participate in the National Olympiad in Informatics in Provinces (NOIP). This competition is only for middle and high school students who have achieved certain results in the second stage of CSP-S. NOIP is similar to the second stage of CSP-S, with a 4.5-hour exam, 4 problems. In NOIP, the top 20% of contestants in each province can receive a first prize.

The third step is the provincial team selection. This competition is only for contestants who have won a first prize in NOIP. Each province selects the top 10 contestants (more precisely, the top 5-17 contestants, depending on the province's quota) from the NOIP first prize winners (50-200 people, depending on the province's competition scale) to participate in the National Olympiad in Informatics.

The fourth step is to participate in the National Olympiad in Informatics. About 300 contestants from across the country participate as official contestants through the provincial teams. The exam lasts two days, with 3 problems each day, and a time limit of 5 hours per day. The top 50 contestants receive gold medals, the 51st to around the 200th contestants receive silver medals, and the rest above top 85% receive bronze medals. The gold medalists form the national training team for special training.

Common websites used by Chinese informatics contestants include Luogu. During holidays, this website sees tens of thousands of active users practicing problems daily. Before CSP-J/S, Luogu's daily submission volume can reach 150,000-250,000. A brief introduction to using Luogu. Based on China's competition system, Luogu classifies problems into the following levels:

【入门难度】（Introductory Level）Suitable for beginners, below or equivalent to Codeforces 800 difficulty.

【普及-】（CSP-J minus）Simple CSP-J problems, equivalent to Codeforces 800~1200 difficulty.

【普及/提高-】（CSP-J/CSP-S minus）Intermediate CSP-J problems, solving these in the competition can earn a first prize, also the difficulty of simple CSP-S problems, equivalent to Codeforces 1200~1600 difficulty.

【普及+/提高】（CSP-J plus/CSP-S/NOIP）Simple to medium difficulty CSP-S and NOIP problems (as difficulty fluctuates in different years), equivalent to Codeforces 1600~2000 difficulty. Solving these problems often results in a first prize in CSP-S or NOIP.

【提高+/省选-】（CSP-S plus/Provincial Team Selection minus）Medium to hard CSP-S and NOIP problems, equivalent to Codeforces 2000~2500 difficulty.

【省选/NOI-】（Provincial Team Selection/NOI minus）Difficult NOIP problems, or simple to medium provincial team selection problems, equivalent to Codeforces 2500~3000. In most provincial team selections, solving these problems gives a good chance of making the provincial team.

【NOI/NOI+/CTSC】（NOI difficulty）Medium to difficult NOI problems, equivalent to Codeforces 3000~3500, or even more difficult. Solving these problems in NOI gives a high probability of winning a gold medal.