28 vector<pair<int,ii>> mst(int n,
 29         vector<pair<int,ii>> edges) {
 30     union_find uf(n);
 31     sort(edges.begin(), edges.end());
 32     vector<pair<int, ii>> res;
 33     rep(i,0,edges.size())
 34         if (uf.find(edges[i].second.first) !=
 35             uf.find(edges[i].second.second)) {
 36             res.push_back(edges[i]);
 37             uf.unite(edges[i].second.first,
 38                      edges[i].second.second); }
 39     return res; }