B3609 [图论与代数结构 701] 强连通分量

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<stack>
using namespace std;
int n,m,tot,head[10010],bel[10010],totb,dfn[10010],low[10010],cnt;
bool tost[10010],vis[10010];
stack<int> st;
vector<int> vct[10010];
struct node{
	int v,next;
}edge[100010];
void make(int u,int v){
	edge[++tot].v=v;
	edge[tot].next=head[u];
	head[u]=tot;
}
void tarjian(int x){
	st.push(x);
	tost[x]=true;
	dfn[x]=low[x]=++cnt;
	for(int i=head[x];i;i=edge[i].next){
		if(!dfn[edge[i].v]){
			tarjian(edge[i].v);
			low[x]=min(low[x],low[edge[i].v]);
		}
		else if(tost[x]){
			low[x]=min(low[x],dfn[edge[i].v]);
		}
	}
	if(low[x]==dfn[x]){
		totb++;
		while(st.top()^x){
			bel[st.top()]=totb;
			vct[totb].push_back(st.top());
			tost[st.top()]=false;
			st.pop();
		}
		st.pop();
		bel[x]=totb;
		vct[totb].push_back(x);
		tost[x]=false;
	}
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;++i){
		int u,v;
		scanf("%d%d",&u,&v);
		make(u,v);
	}
	for(int i=1;i<=n;++i){
		if(!dfn[i]){
			tarjian(i);
		}
	}
	printf("%d\n",totb);
	for(int i=totb;i>=1;--i){
		sort(vct[i].begin(),vct[i].end());
//		int j;
//		for(auto j:vct[i]){
//			printf("%d ",j);
//		}
//		printf("\n");
	}
	for(int i=1;i<=n;++i){
		if(vis[i]) continue;
		int j;
		for(auto j:vct[bel[i]]){
			printf("%d ",j);
			vis[j]=true;
		}
		printf("\n");
	}
	return 0;
}