luogu#P9194. [USACO23OPEN] Triples of Cows P
[USACO23OPEN] Triples of Cows P
题目描述
There are initially pairs of friends among FJ's cows labeled , forming a tree. The cows are leaving the farm for vacation one by one. On day , the th cow leaves the farm, and then all pairs of the th cow's friends still present on the farm become friends.
For each from to , just before the th cow leaves, how many ordered triples of distinct cows are there such that none of are on vacation, is friends with , and is friends with ?
输入格式
The first line contains .
The next lines contain two integers and denoting that cows and are initially friends.
输出格式
The answers for from to on separate lines.
题目大意
给定一棵初始有 个点的树。
在第 天,这棵树的第 个点会被删除,所有与点 直接相连的点之间都会两两连上一条边。你需要在每次删点发生前,求出满足 之间有边, 之间有边且 的有序三元组 对数。
3
1 2
2 3
2
0
0
4
1 2
1 3
1 4
6
6
0
0
5
3 5
5 1
1 4
1 2
8
10
2
0
0
提示
For the first sample:
and are the triples just before cow leaves.
After cow
leaves, there are less than cows left, so no triples are possible.
For the second sample:
At the beginning, cow is friends with all other cows, and no other pairs of
cows are friends, so the triples are where are different cows
from , which gives triples.
After cow leaves, the remaining three cows are all friends, so the triples
are just those three cows in any of the possible orders.
After cow leaves, there are less than cows left, so no triples are
possible.
, .
- Inputs 4-5: .
- Inputs 6-10: .
- Inputs 11-20: No additional constraints.