Tarjan强联通分量【模板】

#include <algorithm>
#include <cstdio>

using namespace std;

const int N(100015);
int n,m,v,u;
int edgesum,head[N];

struct Edge
{
    int from,to,next;
    Edge(int from=0,int to=0,int next=0) :
        from(from),to(to),next(next) {}
}edge[N];
int ins(int from,int to)
{
    edge[++edgesum]=Edge(from,to,head[from]);
    return head[from]=edgesum;
}

int dfn[N],tim,low[N],vis[N];
int Stack[N],top,instack[N];
int col[N],colsum;

void DFS(int now)
{
    dfn[now]=low[now]=++tim; vis[now]=1;
    Stack[++top]=now; instack[now]=1;
    for(int i=head[now];i;i=edge[i].next)
    {
        int to=edge[i].to;
        if(instack[to]) low[i]=min(low[i],dfn[to]);
        else if(!vis[to])
                DFS(to),low[i]=min(low[i],low[to]);
    }
    if(low[now]==dfn[now])
    {
        colsum++;
        col[now]=colsum;
        for(;Stack[top]!=now;top--)
        {
            col[Stack[top]]=colsum;
            instack[Stack[top]]=0;
        }
        instack[now]=0;
        top--;
    }
}

int main()
{
    scanf("%d%d",&n,&m);
    for(;m--;)
    {
        scanf("%d%d",&u,&v);
        ins(u,v);
    }
    for(int i=1;i<=n;i++)
        if(!vis[i]) DFS(i);
    return 0;
}