【luogu2746】 [USACO5.3]校园网Network of Schools [tarjan 缩点]

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define ll long long
 4 const int N=100+5;
 5 int n,in[N],out[N],ans1=0,ans2=0;
 6 int dfn[N],bl[N],low[N],inst[N],sum[N],idx=0,Bcnt=0;
 7 stack<int>s;
 8 template<class t>void rd(t &x){
 9     x=0;int w=0;char ch=0;
10     while(!isdigit(ch)) w|=ch==‘-‘,ch=getchar();
11     while(isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
12     x=w?-x:x;
13 }
14 
15 int tot=0,head[N];
16 struct edge{
17     int u,v,nxt;
18 }e[N*N];
19 void add(int u,int v){
20     e[++tot]=(edge){u,v,head[u]};head[u]=tot;
21 }
22 
23 void tarjan(int u){
24     dfn[u]=low[u]=++idx;
25     inst[u]=1,s.push(u);
26     for(int i=head[u],v;i;i=e[i].nxt){
27         v=e[i].v;
28         if(!dfn[v]) tarjan(v),low[u]=min(low[u],low[v]);
29         else if(inst[v]&&dfn[v]<low[u]) low[u]=dfn[v];
30     }
31     if(dfn[u]==low[u]){
32         ++Bcnt;
33         int v;
34         do{
35             v=s.top();s.pop();
36             bl[v]=Bcnt;
37             ++sum[Bcnt],inst[v]=0;
38         }while(u!=v);
39     }
40 }
41 
42 int main(){
43     freopen("in.txt","r",stdin);
44     rd(n);
45     for(int i=1;i<=n;++i){
46         int v;rd(v);
47         while(v) add(i,v),rd(v);
48     }
49     memset(dfn,0,sizeof(dfn));
50     for(int i=1;i<=n;++i)
51     if(!dfn[i]) tarjan(i);
52     for(int i=1;i<=tot;++i)
53     if(bl[e[i].u]!=bl[e[i].v]) ++in[bl[e[i].v]],++out[bl[e[i].u]];
54     for(int i=1;i<=Bcnt;++i){
55         if(!in[i]) ++ans1;
56         if(!out[i]) ++ans2;
57     }
58     printf("%d\n%d",ans1,Bcnt!=1?max(ans1,ans2):0);
59     return 0;
60 }