Tarjian算法求强联通分量

struct node{
    int v,next;
}e[M];
int head[N],cnt;
int p[N],st[N],id,top,scc;
int dfn[N],low[N],belong[N];
void add(int u,int v){
    e[cnt].v=v,e[cnt].next=head[u];
    head[u]=cnt++;
}
void init(){
    memset(head,-1,sizeof(head));
    memset(p,0,sizeof(p));
    memset(dfn,0,sizeof(dfn));
    id=top=cnt=0;
}
void dfs(int u){
    dfn[u]=low[u]=++id;
    st[++top]=u;p[u]=1;
    int v;
    for(int i=head[u];i!=-1;i=e[i].next){
        v=e[i].v;
        if(!dfn[v]){
            dfs(v);
            if(low[v]<low[u])low[u]=low[v];
        }else if(p[v]&&dfn[v]<low[u]){
            low[u]=dfn[v];
        }
    }
    if(dfn[u]==low[u]){
        ++scc;
        do{
            v=st[top--];
            p[v]=0;
            belong[v]=scc;
        }while(v!=u);
    }
}
void Tarjian(int n){
    for(int i=1;i<=n;i++){
        if(!dfn[i])
            dfs(i);
    }
    printf("%d\n",scc);
    for(int i=1;i<=n;i++){
        printf("%d %d\n",i,belong[i]);
    }
}
int main(){
    int n,m,u,v;
    scanf("%d%d",&n,&m);
    init();
    while(m--){
        scanf("%d%d",&u,&v);
        add(u,v);
    }
    Tarjian(n);
    return 0;
}