2022 7/5 exam summary

Time arrangement

1:20~1:40

T2 Violence is easy to write , I started with violence

1:40~3:00

Feeling T1 It's a routine .
T1 The answer of will not carry more than log Time , Therefore, you can directly enumerate how many bits are entered , Then divide and treat , Add map in , Then enumerate the contributions of one side and then count the contributions of the other side , You can touch it with a large prime number . But for fear of being stuck , Instead of handwritten hash .

3:00~3:40

Pushed T3 The greedy strategy of , And then he wrote 25 branch dfs, Then write down the number of one-dimensional schemes, and you can press dp 了 , Yes 50pts 了 , But the constant is extremely .

3:40~5:00

It is found that the contribution coefficient has nothing to do with the value , So I made a watch , So you can run through 50pts 了 .

5:00~5:40

Beat the watch to find the rules , I didn't expect to find a rule , Feeling T3 can A.
Be on the safe side , Divided into sections

A summary after the exam

T1

Lesson from blood , When the modulus is large , For multiplication int128 Or turtle speed ride
Another problem is that there is no data with a large value range when shooting, resulting in no explosion longlong, The next time you take a pair of shots, the data should be blocked .

T2

1： I didn't expect the combinatorial significance of combinatorial numbers
2： I didn't expect to be divided into blocks
3： I didn't expect that it can be recursive by adding, subtracting, and speeding up the generating function

T3

The place where the watch is written is hung , Instead, it's right to find rules , It's strange to say .
But the proof of the positive solution is also very clever .