tarjan强连通算法

#include <iostream>
#include <string.h>
using namespace std;
const int MAX_N=;
const int MAX_M=;
struct edge{
    int v,next;
    int len;
}E[MAX_M];
int p[MAX_N],eid;
void init(){
    memset(p,-,sizeof(p));
    eid=;
}
void insert(int u,int v){
    E[eid].v=v;
    E[eid].next=p[u];
    p[u]=eid++;
}
 
void tarjan(int u){
    dfn[u]=low[u]=++idx;
    s[top++]=u;
    in_stack[u]=true;
    for(int i=p[u];i+;i=E[i].next){
        int v=E[i].v;
        if(!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }else if(in_stack[v]){
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(dfn[u]==low[u]){
        ++scc;
        do{
            belong[s[--top]]=scc;
            in_stack[s[top]]=false;
        }while(s[top]!=u);
    }
}
int main() {
    int n,m;
    init();
    cin>>n>>m;
    for(int i=;i<m;i++){
        int u,v;
        cin>>u>>v;
        insert(u,v);
    }
    memset(dfn,,sizeof(dfn));
    idx=;
    for(int i=;i<=n;++i){
        if(!dfn[i]){
            tarjan(i);
        }
    }
    for(int i=;i<=scc;i++){
        cout<<"block "<<i<<": ";
        for(int j=;j<=n;j++){
           if(belong[j]==i){
              cout<<j<<" ";
           }
        }
        cout<<endl;
    }
    return ;
}