[Usaco2017 Open]Switch Grass

内存限制：128 MiB 时间限制：10 Sec

Farmer John has recently been experimenting with cultivating different types of grass on his farm, r

ealizing that different types of cows like different types of grass. However, he must be careful to

ensure that different types of grass are planted sufficiently far away from each-other, in order to

prevent them from being inextricably mixed.FJ's farm consists of Nfields (1≤N≤200,000), where M pa

irs of fields are connected by bi-directional pathways (1≤M≤200,000). Using these pathways, it is

possible to walk from any field to any other field. Each pathway has an integer length in the range

1…1,000,000. Any pair of fields will be linked by at most one direct pathway.In each field, FJ init

ially plants one of Ktypes of grass (1≤K≤N). Over time, however, he might decide to switch the gra

ss in some field to a different type. He calls this an "update" operation. He might perform several

updates over the course of time, which are all cumulative in nature.After each update, FJ would like

to know the length of the shortest path between two fields having different grass types. That is, a

mong all pairs of fields having different grass types, he wants to know which two are closest. Ideal

ly, this number is large, so he can prevent grass of one type from mixing with grass of another type

. It is guaranteed that the farm will always have at least two fields with different grass types.In

30 percent of the input cases, each field will be directly connected to at most 10 pathways.

给定一张带权无向图，每个点有一个颜色，每次改变一个点的颜色，要求你在操作后输出这个图中最近异色点对之

间的距离最近异色点对定义为：一对点颜色不同，且距离最小

The first line of input contains four integers, N, M, K, and Q, where Q is the number of updates (1

≤Q≤200,000). The next M lines describe the paths; each one contains three integers A, B, and L, in

dicating a path from field A to field B (both integers in the range 1…N) of length L. The next line

indicates the initial type of grass growing in each field (N integers in the range 1…K). Finally,

the last Q lines each describe an update, specified by two integers A and B, where the grass in fiel

d A is to be updated to type B

For each update, print the length of the shortest path between two fields with different types of grass

after the update is applied.

#4777. [Usaco2017 Open]Switch Grass