Hawk-and-Chicken 强连通

#include<bits/stdc++.h>
using namespace std;
//input by bxd
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define repp(i,a,b) for(int i=(a);i>=(b);--i)
#define RI(n) scanf("%d",&(n))
#define RII(n,m) scanf("%d%d",&n,&m)
#define RIII(n,m,k) scanf("%d%d%d",&n,&m,&k)
#define RS(s) scanf("%s",s)
#define ll long long
#define pb push_back
#define CLR(A,v)  memset(A,v,sizeof A)
//////////////////////////////////
#define inf 0x3f3f3f3f
const int N=50000+5;
int head[N*6],pos;
vector<int> mp[N];
struct Edge
{
    int to,nex;
}edge[N*6];
void add(int a,int b)
{
    edge[++pos].nex=head[a];
    head[a]=pos;
    edge[pos].to=b;
}
int ind,tot,cnt,dfn[N],low[N],vis[N],belong[N],Stack[N],num[N],in[N],dis[N],out[N];
void init()
{
    ind=tot=pos=cnt=0;
    CLR(Stack,0);
    CLR(out,0);
    CLR(dis,0);
    CLR(in,0);
    CLR(num,0);
    CLR(dfn,0);
    CLR(low,0);
    CLR(vis,0);
    CLR(head,0);
}
void tarjan(int x)
{
    dfn[x]=low[x]=++tot;
    Stack[++ind]=x;
    vis[x]=1;
    for(int i=head[x];i;i=edge[i].nex)
    {
        int v=edge[i].to;
        if(!dfn[v])
        {
            tarjan(v);
            low[x]=min(low[x],low[v]);
        }
        else if(vis[v])
            low[x]=min(low[x],low[v]);

    }
    if(low[x]==dfn[x])
    {
        cnt++;int v;
        do
        {
            v=Stack[ind--];
            vis[v]=0;
            num[cnt]++;
            belong[v]=cnt;
        }
        while(v!=x);
    }
}
int Cnt;
void dfs(int x)
{
    Cnt+=num[x];
    if(mp[x].size())
    rep(i,0,mp[x].size()-1)
    {
        int v=mp[x][i];
        if(vis[v])continue;
        vis[v]=1;
        dfs(v);
    }
}

int main()
{
    int cas;
    RI(cas);
    int T=0;
    while(cas--)
    {
        init();
        int n,m;
        RII(n,m);
        rep(i,1,m)
        {
            int a,b;
            RII(a,b);
            a++;b++;
            add(a,b);
        }

    rep(i,1,n)
    if(!dfn[i])tarjan(i);

    rep(i,1,n)
    {
        int u=belong[i];
        for(int j=head[i];j;j=edge[j].nex)
        {
            int v=belong[ edge[j].to ];

            if(u!=v)
                in[v]++,mp[v].pb(u),out[u]++;
        }
    }
    int maxx=0;

    rep(i,1,cnt)
    if(out[i]==0)
    {
        Cnt=0;
        CLR(vis,0);
        dfs(i);
        dis[i]=Cnt;

        if(Cnt>maxx)
        {
            maxx=Cnt;
        }
    }
    rep(i,1,cnt)
    maxx=max(maxx,dis[i]);

    printf("Case %d: %d\n",++T,maxx-1);
    int first=1;
    rep(i,1,n)
    {
        int u=belong[i];
        if(dis[u]==maxx)
        {
            if(first)
                first=0,printf("%d",i-1);
            else printf(" %d",i-1);
        }
    }
    cout<<endl;
    rep(i,1,cnt)
    mp[i].clear();
    }
    return 0;

}