[洛谷1346]电车

 1 #include<cstdio>
 2 #include<cctype>
 3 #include<vector>
 4 #include<algorithm>
 5 #include<functional>
 6 #include<ext/pb_ds/priority_queue.hpp>
 7 inline int getint() {
 8     char ch;
 9     while(!isdigit(ch=getchar()));
10     int x=ch^‘0‘;
11     while(isdigit(ch=getchar())) x=(((x<<2)+x)<<1)+(ch^‘0‘);
12     return x;
13 }
14 const int N=101,inf=0x7fffffff;
15 struct Edge {
16     int to,w;
17     bool operator > (const Edge &x) const {
18         return w>x.w;
19     }
20 };
21 std::vector<int> e[N];
22 int w[N][N];
23 inline void add_edge(const int u,const int v,const int ww) {
24     e[u].push_back(v);
25     w[u][v]=ww;
26 }
27 int d[N]= {0};
28 bool v[N]= {0};
29 int main() {
30     int n=getint(),a=getint(),b=getint();
31     for(int i=1; i<=n; i++) {
32         int k=getint();
33         for(int j=0; j<k; j++) {
34             add_edge(i,getint(),j?1:0);
35         }
36     }
37     __gnu_pbds::priority_queue<Edge,std::greater<Edge> > q;
38     __gnu_pbds::priority_queue<Edge,std::greater<Edge> >::point_iterator p[n+1];
39     for(int i=1; i<=n; i++) p[i]=q.push((Edge){i,d[i]=(i==a)?0:inf});
40     for(int i=0; i<n; i++) {
41         Edge u=q.top();
42         if(u.w==inf) break;
43         for(unsigned int j=0; j<e[u.to].size(); j++) {
44             if(v[e[u.to][j]]) continue;
45             int &v=e[u.to][j];
46             q.modify(p[v],(Edge) {
47                 v,d[v]=std::min(p[v]->w,u.w+w[u.to][v])
48             });
49         }
50         q.modify(p[u.to],(Edge){u.to,inf});
51         v[u.to]=true;
52     }
53     printf("%d\n",(d[b]==inf)?-1:d[b]);
54     return 0;
55 }