P1346 电车

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int maxn=10000;
 4 const int maxm=50000;
 5 const int INF=1e9;
 6 
 7 inline int read()
 8 {
 9     int x=0,k=1;char c=getchar();
10     while(c<‘0‘||c>‘9‘) {if(c==‘-‘) k=-1;c=getchar();}
11     while(c>=‘0‘&&c<=‘9‘) x=(x<<3)+(x<<1)+(c^48),c=getchar();
12     return x*k;
13 }
14 
15 int cnt,dis[maxn],vis[maxn],head[maxm],n,m,s,t;
16 
17 struct Edge{
18     int u,v,w,next;
19 }e[maxm];
20 
21 inline void add(int u,int v,int w)
22 {
23     e[++cnt].u=u;
24     e[cnt].v=v;
25     e[cnt].w=w;
26     e[cnt].next=head[u];
27     head[u]=cnt;
28 }
29 
30 struct node{
31     int w,now;
32     inline bool operator <(const node& x) const
33     {
34     return w>x.w;
35     }
36 };
37 
38 priority_queue<node> q;
39 
40 void dijikstra()
41 {
42     for(int i=1;i<=n;++i) dis[i]=INF;
43     dis[s]=0;
44     q.push((node){0,s});
45     while(!q.empty())
46     {
47         node x=q.top();
48         q.pop();
49         int u=x.now;
50         if(vis[u]) continue;
51         vis[u]=1;
52         for(int i=head[u];i;i=e[i].next)
53         {
54             int v=e[i].v;
55             if(dis[v]>dis[u]+e[i].w)
56             {
57                 dis[v]=dis[u]+e[i].w;
58                 q.push((node){dis[v],v});
59             }
60         }
61     }
62 }
63 
64 int main()
65 {
66     n=read(),s=read(),t=read();
67     for(int i=1,x,y,z;i<=n;++i)
68     {
69         x=read();
70         for(int j=1;j<=x;++j)
71         {
72             y=read();
73             if(j==1) add(i,y,0);
74             else add(i,y,1);
75         }
76    }
77    dijikstra();
78    if(dis[t]>=INF)  printf("-1");
79    else printf("%d",dis[t]);
80    return 0;
81 }