To summarize the recent case of two exams.
11.6 Field
Opening first read the title, T1 feel like searching, T2 graph theory no idea, T3 did not understand the question. Further analysis of what a sample of T3, be considered to get to know the title, feel relatively T3 do, do questions to determine the order of 3-1-2. Initially wanted to use dsu on tree + Fenwick tree, but it feels good to clear the existing information, there is no want to continue down, so he naturally thought of the tree line merger, the space is a little tight, forget about the space, the node can be recovered too. 1h write and debug completed T3, take it to shoot, opened T1, and then open test about 1.5h. A rough calculation and T1 time complexity is $ 3 ^ {25} $, feeling no, then remembered (jsq reminder) can binary search, search after sorting, double pointer statistical answer that he constructed several sets of data, running a bit, feeling no problem, statically checked again wrong, it seems to have no problem to open T2, and then from the end of the examination left about 1h. Began to think T2, half of it is clear, but it will not check, suppose a conclusion yet own their own hack, so I started to play violent left in 30min when constructed several small data seems to be no problem, went to check the file name and the size of the array.
Desirable Score: 100 + 30 + 100 = 230
Actual Score: 100 + 20 + 100 = 220
T1 no problem.
T2 does exist a conclusion, we did not expect to see the kinds of questions or less. Violence linked to the fight because then lead the table size is not clear when each map was built.
Positive Solutions of T3 is dfs order + Fenwick tree, in fact, I think dsu on the tree have thought dfs order, but feel bad answer-time statistics, the statistical result is three separate answer, as this is the case time and segment tree merger is O (N logN), but better than the space segment tree is merged O (N). Inflexible thinking or feeling, thinking all the answers figured out the one-time, in fact, so difficult, but if a little flexible, then thought to think several separate statistical answer.
11.7 Field
Opening first read the title, T1 feel monotonous stack, T2 no idea, T3 is determined DAG ... do question the order of 1-3-2. T1 is a ring, there are two arcs between two points on the ring, feeling good statistics, so directly off the chain ring twice, instead monotonous queue maintenance, but if there is high with ice picks and difficult to maintain, so he opened a queue, a queue corresponding to the first record of the number of picks which is the same height, but deleted when the time will go wrong, so he maintains a linked list, then the statistical answer, and finally to heavy, over a sample, of their own hands rub a few sets of data, have not been found, static troubleshooting, think of the problem, the details are not well thought out, changed a bit, they had a special hand-made their own data, and then output a number of arrays and found no problems, T3 opened up. Drew a drawing, no feeling, thinking a bit chaotic, went to the second bathroom to calm down, and then to give up T3, want to T2, a little push a bit and found that DP, then the relationship p appears to be forest, then another to maintain a root conjugated on the end, over a sample, not seen two examples, a number of output values of the intermediate, found a little problem, changed to change over, then left for 1 hour. Although T3 may look like half way, but two points toward thought necessary to extract all the path length greater than the mid feeling feasible, went properties. Even have a conclusion, it seems that as long break at the start or end on it, and quickly write, finished only to find that wrong, but the time was too late to give up. Checked arrays, and file name on an assignment.
Desirable Score: 0 + 100 + 100 = 200
Actual Score: 100 + 100 + 5 = 205
The first Gufen lower than the actual score ...
T1 appears to be directly on the line monotonically stack, but the position of the ring must be broken is the highest point.
T2 make trouble, and you can maintain a prefix
T3, again died on the DAG. In fact, before the dichotomous approach is feasible, a predetermined maximum two topological sorting deposit to the starting point with the maximum value to the end, half the time to enumerate watching whether it is necessary to extract, extracted from all sides and then decided whether or not to go through point on it. Of course, practice is also very clever solution to a problem, the use of topological order hierarchical thinking, dynamic data structure maintenance, this approach seems to be the first time I saw it.
to sum up
Two-day exam died on the topic map, and all DAG, his view of the topic or do less, in recent years noip practice questions and DP question, after which need to practice my drawing topic, especially the application of graph theory questions the basic algorithm. Next week on the exam, ltw these two days have AK, and his strength is in urgent need of upgrade ah.
2019-11-07