tarjan有向图模板

void tarjan(int x)
{
    num++;
    dfn[x]=low[x]=num;
    vis[x]=true;
    st[++top]=x;
    for(int i=firstt[x];i;i=nextt[i])
    {
        int y=to[i];
        if(dfn[y]==0)
        {
            tarjan(y);
            low[x]=min(low[x],low[y]);
        }
        else if(vis[y]==true) low[x]=min(low[x],dfn[y]); 
    }
    if(low[x]==dfn[x])
    {
        int y;
        lhy++;
        do
        {
            y=st[top--];
            color[y]=lhy;
            vis[y]=false;
            sum[lhy]++;
        }while(x!=y);
    }
}