PKU 1847 Tram

有向图，有联系的点之间连边，如果是第一个领接的点，则边的权值为0，后面领接点边的权值为1，建图后做SPFA。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define oo  0x7f7f7f7f
using namespace std;
const int N = 110;
struct Edge
{
    int to,dis;
    Edge * next;
};
Edge *adj[N];
Edge edge[N*N];
bool vis[N];
int dis[N];
int cnt;
void addEdge(int u,int v,int w)
{
    Edge *ptr = &edge[cnt++];
    ptr->to = v;
    ptr->dis = w;
    ptr->next = adj[u];
    adj[u] = ptr;
}
int n,st,ed;
int spfa()
{
    queue <int> Q;
    memset(vis,false,sizeof(vis));
    memset(dis,127,sizeof(dis));
    dis[st] = 0;
    Q.push(st);
    while(!Q.empty())
    {
        int u = Q.front();Q.pop();
        vis[u] = false;
        for(Edge*ptr = adj[u];ptr;ptr=ptr->next)
        {
            int v = ptr->to;
            if(dis[v]>dis[u]+ptr->dis)
            {
                dis[v] = dis[u] + ptr->dis;
                 if(!vis[v])
                 {
                    Q.push(v);
                    vis[v] = true;
                 }
            }
        }
    }
    if(dis[ed]<oo)
    {
        return dis[ed];
    }
    else
    {
        return -1;
    }




}
int main()
{
    cnt = 0;
    scanf("%d%d%d",&n,&st,&ed);
    for(int i=1;i<=n;i++)
    {
        int ki;
        scanf("%d",&ki);
        for(int j=1;j<=ki;j++)
        {
            int v;
            scanf("%d",&v);
            if(j==1)
            {
                addEdge(i,v,0);
            }
            else
            {
                addEdge(i,v,1);
            }
        }
    }
       printf("%d\n",spfa());
    return 0;
}