| 1 | #include "../data-structures/union_find.cpp" |
| 2 | struct arborescence { |
| 3 | int n; union_find uf; |
| 4 | vector<vector<pair<ii,int> > > adj; |
| 5 | arborescence(int _n) : n(_n), uf(n), adj(n) { } |
| 6 | void add_edge(int a, int b, int c) { |
| 7 | adj[b].push_back(make_pair(ii(a,b),c)); } |
| 8 | vii find_min(int r) { |
| 9 | vi vis(n,-1), mn(n,INF); vii par(n); |
| 10 | rep(i,0,n) { |
| 11 | if (uf.find(i) != i) continue; |
| 12 | int at = i; |
| 13 | while (at != r && vis[at] == -1) { |
| 14 | vis[at] = i; |
| 15 | iter(it,adj[at]) if (it->second < mn[at] && |
| 16 | uf.find(it->first.first) != at) |
| 17 | mn[at] = it->second, par[at] = it->first; |
| 18 | if (par[at] == ii(0,0)) return vii(); |
| 19 | at = uf.find(par[at].first); } |
| 20 | if (at == r || vis[at] != i) continue; |
| 21 | union_find tmp = uf; vi seq; |
| 22 | do { seq.push_back(at); at = uf.find(par[at].first); |
| 23 | } while (at != seq.front()); |
| 24 | iter(it,seq) uf.unite(*it,seq[0]); |
| 25 | int c = uf.find(seq[0]); |
| 26 | vector<pair<ii,int> > nw; |
| 27 | iter(it,seq) iter(jt,adj[*it]) |
| 28 | nw.push_back(make_pair(jt->first, |
| 29 | jt->second - mn[*it])); |
| 30 | adj[c] = nw; |
| 31 | vii rest = find_min(r); |
| 32 | if (size(rest) == 0) return rest; |
| 33 | ii use = rest[c]; |
| 34 | rest[at = tmp.find(use.second)] = use; |
| 35 | iter(it,seq) if (*it != at) |
| 36 | rest[*it] = par[*it]; |
| 37 | return rest; } |
| 38 | return par; } }; |
| 39 | // vim: cc=60 ts=2 sts=2 sw=2: |
nothing calls this directly
no outgoing calls
no test coverage detected