luogu P1346 电车 最短路

#include<map>
#include<queue>
#include<time.h>
#include<limits.h>
#include<cmath>
#include<ostream>
#include<iterator>
#include<set>
#include<stack>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define rep_1(i,m,n) for(int i=m;i<=n;i++)
#define mem(st) memset(st,0,sizeof st)
int read()
{
	int res=0,ch,flag=0;
	if((ch=getchar())=='-')             //判断正负
		flag=1;
	else if(ch>='0'&&ch<='9')           //得到完整的数
		res=ch-'0';
	while((ch=getchar())>='0'&&ch<='9')
		res=res*10+ch-'0';
	return flag?-res:res;
}
typedef long long ll;
typedef pair<int,int> pii;
typedef unsigned long long ull;
typedef pair<double,double> pdd;
const int inf = 0x3f3f3f3f;
const int N=101010;
int e[N],ne[N],idx,h[N],w[N];
int n,a,b; 
int dist[N];
int st[N];
void add(int a,int b,int c)
{
	e[idx]=b;
	w[idx]=c;
	ne[idx]=h[a];
	h[a]=idx++;
}
void spfa(int start)
{
	queue<int>q;
	q.push(start);
	dist[start]=0;
	st[start]=1;
	while(q.size())
	{
		int t=q.front();
		q.pop();
		st[t]=0;
		for(int i=h[t];i!=-1;i=ne[i])
		{
			int j=e[i];
			if(dist[j]>dist[t]+w[i])
			{
				dist[j]=dist[t]+w[i];
				if(!st[j])
				{
					q.push(j);
					st[j]=1;
				}
			}
		}
	}
}
int main()
{
	memset(h,-1,sizeof h);
	cin>>n>>a>>b;
	for(int i=1;i<=n;i++)
	{
		int m;
		cin>>m;
		for(int j=1;j<=m;j++)
		{
			int x;
			cin>>x;
			if(j==1)
				add(i,x,0);
			else
				add(i,x,1); 
		}
	}
	memset(dist,0x3f,sizeof dist);
	spfa(a);
	if(dist[b]>=0x3f3f3f3f)
		cout<<"-1"<<endl;
	else
		cout<<dist[b]<<endl;
	return 0;
}