【模板】Tarjan

#include<bits/stdc++.h>
#define MAX 5005
using namespace std;
int n,m,low[MAX],dfn[MAX],top=0,dnum=0,sta[MAX],howmany=0,color[MAX];
bool vis[MAX]={0};
vector<int>G[MAX];
void Tarjan(int u)
{
    dfn[u]=++dnum;
    vis[u]=true;
    low[u]=dnum;
    sta[++top]=u;
    for(int i=0;i<G[u].size();i++)
    {
        int v=G[u][i];
        if(!dfn[v])
        {
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(vis[v])low[u]=min(low[u],dfn[v]);
    }
    if(dfn[u]==low[u])
    {
        vis[u]=false;
        color[u]=++howmany;
        while(sta[top]!=u)
        {
            color[sta[top]]=howmany;
            vis[sta[top--]]=false;
        }
        top--;
    }
}
int main()
{
    int a,b;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&a,&b);
        G[a].push_back(b);
    }
    Tarjan(1);
    printf("%d\n",howmany);
    for(int i=1;i<=n;i++)cout<<i<<" "<<color[i]<<endl;
    return 0;
}