模板—e-dcc缩点

int dfn[MAXN],low[MAXN],cnt;
bool isbridge[MAXN];
void tarjan(int x,int edg)
{
    low[x]=dfn[x]=++cnt;
    for(int i=f(x);i;i=n(i))
    if(!dfn[v(i)])
    {
        tarjan(v(i),i);
        low[x]=min(low[x],low[v(i)]);
        if(low[v(i)]>dfn[x])
            isbridge[i]=isbridge[i^1]=1;
    }
    else if(i!=(edg^1))low[x]=min(low[x],dfn[v(i)]);
}
int c[MAXN],dcc;
void dfs(int x,int dcc)
{
    c[x]=dcc;
    for(int i=f(x);i;i=n(i))
    if(!c[v(i)]&&!isbridge[i])
        dfs(v(i),dcc);
}
signed main()
{
    for(int i=1;i<=n;i++)
    if(!dfn[i])tarjan(i,0);
    for(int i=1;i<=n;i++)
    if(!c[i])dcc++,dfs(i,dcc);
    for(int i=2;i<=num_e;i++)
    if(c[u(i)]!=c[v(i)])
        du[c[u(i)]]++;
}