USACO 3.2 Sweet Butter(SPFA）

/*
ID: cuizhe
LANG: C++
TASK: butter
*/
#include <cstdio>
#include <cstring>
#include <cmath>
#include <queue>
using namespace std;
#define INF 0x3f3f3f3f
int first[1001],cow[1001],t,p,d[1001],in[801];
int dis[801][801];
queue<int> que;
struct node
{
int u,v,w,next;
}edge[5001];
void CL()
{
t = 1;
memset(first,-1,sizeof(first));
}
void add(int u,int v,int w)
{
edge[t].u = u;
edge[t].v = v;
edge[t].w = w;
edge[t].next = first[u];
first[u] = t;
t ++;
}
void spfa(int str)//以后变量的统统都是这样写了。
{
int i,v,u;
for(i = 1;i <= p;i ++)
{
in[i] = 0;
d[i] = INF;
}
que.push(str);
in[str] = 1;
d[str] = 0;
while(!que.empty())
{
u = que.front();
in[u] = 0;
que.pop();
for(i = first[u];i != -1;i = edge[i].next)
{
v = edge[i].v;
if(d[v] > d[u]+edge[i].w)
{
d[v] = d[u]+edge[i].w;
if(!in[v])
{
in[v] = i;
que.push(v);
}
}
}
}
for(i = 1;i <= p;i ++)
{
dis[str][i] = d[i];
dis[i][str] = d[i];
}
}
int main()
{
int i,j,n,c,ans,sum,sv,ev,w;
freopen("butter.in","r",stdin);
freopen("butter.out","w",stdout);
scanf("%d%d%d",&n,&p,&c);
CL();
for(i = 1;i <= p;i ++)
{
for(j = 1;j <= p;j ++)
dis[i][j] = INF;
dis[i][i] = 0;
}
for(i = 1;i <= n;i ++)
{
scanf("%d",&cow[i]);
}
for(i = 1;i <= c;i ++)
{
scanf("%d%d%d",&sv,&ev,&w);
add(sv,ev,w);
add(ev,sv,w);
}
for(i = 1;i <= n;i ++)
{
spfa(cow[i]);
}
ans = INF;
for(i = 1;i <= p;i ++)
{
sum = 0;
for(j = 1;j <= n;j ++)
{
if(dis[i][cow[j]] == INF)
break;
sum += dis[i][cow[j]];
}
if(j == n+1)
{
if(ans > sum)
ans = sum;
}
}
printf("%d\n",ans);
return 0;
}