Foreword As a major competition connecting enterprises and universities, the Blue Bridge Cup has a great importance in major universities. The awards of this competition during the university period are also very high, which is a great affirmation of personal ability. The competition in the Blue Bridge Cup is also very huge. To win the prize, you must not only have outstanding ability, but also need to use the correct method to understand the knowledge points and difficult parts. These are the basic essentials of winning. Below, the author analyzes the knowledge points and difficulty of the Blue Bridge Cup Group B topics in the past three years. Difficulty Analysis We roughly divide these questions into three levels of difficulty: low, medium, and high. Low difficulty is a score-giving question, and most of them are fill-in-the-blank questions. You only need to submit the answer when answering. First of all, low-difficulty questions, which generally only need to submit a number or a string to fill in the blanks, are to test the candidates' general logical thinking ability and the application of general mathematics and programming. The medium difficulty is the largest part. It consists of individual fill-in-the-blank questions and a large number of programming questions. Questions of this difficulty will consume a lot of time for candidates, and obstacles will be set up in the corresponding programming questions, so that each question in the test will be scored. gap. This obstacle is generally reflected in the optimization of time complexity. The lower the time complexity, the higher the score of this question will be. For example, take the fifth question of Group B in 2019 as an illustration, the question is as follows: Given three integer arrays
A = [A1, A2, ... AN],
B = [B1, B2, ... BN],
C = [C1, C2, ... CN]，
Please count how many triples (i, j, k) satisfy:
1. 1 <= i, j, k <= N
2. Ai < Bj < Ck When I saw this question, three layers of for loop violently appeared in my mind, but this would only get one-third of the points. If you want to get the full score, another time complexity is needed. Low loop, this question should use two two-layer for loops to get full marks. Finally, there are difficult questions. These questions are generally prepared for students who are entering the national and international competitions. The characteristics of such questions are difficult. However, it is not impossible to solve the problem. It is still possible to complete the problem within a limited time by comprehensively using the algorithm and analyzing the problem comprehensively. For example, the ninth question of the 2020 simulation competition sequence counting, this question requires proficient mastery of DFS and BFS, and on this basis, memory search can be used to pass 80% of the sample data. Knowledge point analysis The author counted the simulation questions of 18 years, 2019 group B and 20 years. It can basically be determined that the first two questions are easy to send points, there are 5 and 6 questions in the middle, and the last three questions are high. Difficulty questions. Low-difficulty topics cover knowledge points including various unit conversion, time conversion, statistical calculation and other low-difficulty knowledge, so I will not elaborate. The medium difficulty covers many problems that require logical thinking, and the requirements for various algorithms are not high. Most of the problems of this difficulty can be solved by violent enumeration, but the number of for loop layers exceeds three layers and must be optimized. Secondly, the two search algorithms, DFS and BFS, are also common test sites, such as the 19-year maze. Hash tables and double pointers are also frequently tested, as well as various sorting algorithms and greedy algorithms, which often appear in this part of the subject. Among the difficult topics, the two major search algorithms, DFS and BFS, also appear frequently. In addition, there are dynamic programming, backtracking algorithms, etc. Some topics also involve divide-and-conquer strategies, which are combined with other ways of thinking. , it is very difficult to get a full score, and the focus should still be placed on the first two difficult questions.
To sum up, the knowledge points of each difficulty are mainly involved as follows;
(1) Low: general mathematical knowledge and logical thinking
(2) Medium: Enumeration, DFS, BFS, Hash Table, Double Pointer, Greedy Algorithm, Major Sorting Algorithms
(3) High: DFS, BFS, dynamic programming, backtracking algorithm, divide-and-conquer strategy. General students participate in the Blue Bridge Cup and do their best to solve the problems of low and medium difficulty. So how to overcome the time complexity problem in medium difficulty? Just look for leetcode. If the time complexity is not optimal, it is not allowed to submit. It is very effective to practice questions on it. END
Editor-in-Chief | Wang Nanlan
Editor in Charge | The stronger Liu Shihao's ability, the greater his responsibility. Seek truth from facts, rigorous and meticulous.
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