Mathematics: Orsay Classics (published by Shen Wenxuan of Hunan Normal University, etc. ), Complete Works of Solving Olympic Games Problems in Senior High School (edited by Zhou Peigeng and Wang), Little Series of Mathematical Olympiad (published by East China Normal University), Journal of Secondary Mathematics (published by Tianjin Normal University) and Elementary Number Theory (published by Pan Chengdong and Pan Cheng Biao, published by Peking University).

If you just want to know some competition knowledge, it is enough to choose one from the Olympic Games classics and the high school Olympic Games problem-solving encyclopedia. But if you want to enter the winter camp and win prizes, you'd better buy both elementary number theory and Olympic series to learn some advanced mathematics knowledge. In fact, the knowledge of extracurricular competitions is not the most important. The most important thing is to establish and gradually improve the thinking system of solving competition problems by doing problems. If you want to make great achievements in the competition, I suggest you start from grade one, don't rush to do a lot of competition questions, and strive to learn math knowledge by yourself in grade one. From the second year of senior high school, you will learn a lot of competition knowledge and do the questions one by one, so at least it is not a problem to win the first place in the league. Whether you can get good grades in winter camp depends on your luck.