void topo_sort(IV &in, IV &order) {
IQ q;
for (int i = 0; i < n; ++i) if (in[i] == 0) q.push(i);
order.clear();
while (! q.empty()) {
int v = q.front(); q.pop();
order.push_back(v);
cFor (EL, e, adj[v])
if (--in[e->v] == 0) q.push(e->v);
}
}
