#P3006. [USACO11JAN] Bottleneck G
[USACO11JAN] Bottleneck G
题目描述
Farmer John is gathering the cows. His farm contains a network of N (1 <= N <= 100,000) fields conveniently numbered 1..N and connected by N-1 unidirectional paths that eventually lead to field 1. The fields and paths form a tree.
Each field i > 1 has a single one-way, exiting path to field P_i, and currently contains C_i cows (1 <= C_i <= 1,000,000,000). In each time unit, no more than M_i (0 <= M_i <= 1,000,000,000) cows can travel from field i to field P_i (1 <= P_i <= N) (i.e., only M_i cows can traverse the path).
Farmer John wants all the cows to congregate in field 1 (which has no limit on the number of cows it may have). Rules are as follows:
* Time is considered in discrete units.
* Any given cow might traverse multiple paths in the same time unit. However, no more than M_i total cows can leave field i (i.e., traverse its exit path) in the same time unit.
* Cows never move *away* from field #1.
In other words, every time step, each cow has the choice either to
a) stay in its current field
b) move through one or more fields toward field #1, as long as the bottleneck constraints for each path are not violated
Farmer John wants to know how many cows can arrive in field 1 by certain times. In particular, he has a list of K (1 <= K <= 10,000) times T_i (1 <= T_i <= 1,000,000,000), and he wants to know, for each T_i in the list, the maximum number of cows that can arrive at field 1 by T_i if scheduled to optimize this quantity.
Consider an example where the tree is a straight line, and the T_i list contains only T_1=5, and cows are distibuted as shown:
Locn: 1---2---3---4 <-- Pasture ID numbers
C_i: 0 1 12 12 <-- Current number of cows
M_i: 5 8 3 <-- Limits on path traversal; field 1 has no limit since it has no exit
The solution is as follows; the goal is to move cows to field 1:
Tree: 1---2---3---4
t=0 0 1 12 12 <-- Initial state
t=1 5 4 7 9 <-- field 1 has cows from field 2 and 3 t=2 10 7 2 6
t=3 15 7 0 3
t=4 20 5 0 0
t=5 25 0 0 0
Thus, the answer is 25: all 25 cows can arrive at field 1 by time t=5.
## 输入格式
\* Line 1: Two space-separated integers: N and K
\* Lines 2..N: Line i (not i+1) describes field i with three
space-separated integers: P\_i, C\_i, and M\_i
\* Lines N+1..N+K: Line N+i contains a single integer: T\_i
## 输出格式
\* Lines 1..K: Line i contains a single integer that is the maximum number of cows that can arrive at field 1 by time T\_i.
```input1
4 1
1 1 5
2 12 7
3 12 3
5
25