If the competition is to win a prize, I suggest taking a look at college probability theory (if conditions permit). Inequality, I suggest you be very proficient in important theorems about inequality, such as Cauchy inequality, absolute value inequality and so on. If you are just a beginner in the competition, I think the series of books published by Shanghai Jiaotong University is very good. If you want to break through, calculus is also strong. The limit of a university is very important, and some difficult problems require extreme knowledge. One year, the last question of the Beijing College Entrance Examination involved this knowledge. You can look at Advanced Mathematics (6th Edition) of Tongji University. This version is relatively simple. In fact, do you know that the knowledge learned by the masters of the competition is even higher than the learning requirements of the university to some extent? You will know a lot at first glance, but you have to reach this level, prove every theorem on the certificate (there is a simple proof process), and then do every question to know the formula to be used, so as to improve in the competition. Finally, if you are interested in fighting, I wish you good results.