Connect the Cities 【最小生成树】

In 2100, since the sea level rise, most of the cities disappear. Though some survived cities are still connected with others, but most of them become disconnected. The government wants to build some roads to connect all of these cities again, but they don’t want to take too much money.
Input
The first line contains the number of test cases.
Each test case starts with three integers: n, m and k. n (3 <= n <=500) stands for the number of survived cities, m (0 <= m <= 25000) stands for the number of roads you can choose to connect the cities and k (0 <= k <= 100) stands for the number of still connected cities.
To make it easy, the cities are signed from 1 to n.
Then follow m lines, each contains three integers p, q and c (0 <= c <= 1000), means it takes c to connect p and q.
Then follow k lines, each line starts with an integer t (2 <= t <= n) stands for the number of this connected cities. Then t integers follow stands for the id of these cities.
Output
For each case, output the least money you need to take, if it’s impossible, just output -1.
Sample Input
1
6 4 3
1 4 2
2 6 1
2 3 5
3 4 33
2 1 2
2 1 3
3 4 5 6
Sample Output
1
题意 n个点m条路，其中有一些点之间已经连接在一起，问最少需要多少钱。
已经链接在一起的点，可以用并查集来搞，然后在跑一个MST
代码

#include<bits/stdc++.h>#define  LL long longusing  namespace std;const  int MAXN = 1e5;const  int  MAXM = 1e8;const  double PI = acos(-1.0);const double e =exp(1.0);/*-------------------------------*/struct  Edge {    int from,to,val;}edge[MAXN];bool  cmp(Edge  a,Edge b){    return a.val<b.val;}int par[MAXN];int n,m,k;int Find(int x){return x==par[x]?x:par[x]=Find(par[x]);}void join(int a,int  b){    a=Find(a);    b=Find(b);    if(a!=b) par[a]=b;}void init(){    for(int i=0;i<=n;i++)        par[i]=i;}void getmap(){    int a,b,c;    for(int i=0;i<m;i++)        scanf("%d%d%d",&edge[i].from,&edge[i].to,&edge[i].val);    while(k--){        int t;scanf("%d",&t);            t--;scanf("%d",&a);            while(t--){                scanf("%d",&b);                join(a,b);            }    }}void krus(){    int  sum=0;    sort(edge,edge+m,cmp);    for(int  i=0;i<m;i++){        Edge  e=edge[i];        if(Find(e.from)!=Find(e.to)) {            sum+=e.val;            join(e.from,e.to);        }    }    int i,j;    for(i=2;i<=n;i++){        if(Find(i)!=Find(1)) break;    }    if(i==n+1)    printf("%d\n",sum);    else printf("-1\n");}int  main(){    int t;cin>>t;    while(t--){        scanf("%d%d%d",&n,&m,&k);        init();        getmap();        krus();    }    return 0;}