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Add graph/virtual_tree.cc

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subcrip 2024-09-05 23:27:47 +08:00
parent 7e9f23f8e7
commit 47fcbd6011
1 changed files with 53 additions and 0 deletions
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graph/virtual_tree.cc Normal file
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// BUG: unchecked code
struct virtual_tree {
int n, root;
vector<vector<pil>> e;
LCA lca;
vector<int> dfn;
vector<ll> ps;
virtual_tree(const vector<vector<pil>>& e, int root) : n(e.size() - 1), root(root), e(e), lca(vector<vector<int>> {{}, {}}), dfn(n + 1), ps(n + 1) {
vector<vector<int>> ch(n + 1);
for (int u = 0; u <= n; ++u) {
for (auto&& [v, w] : e[u]) {
ch[u].emplace_back(v);
}
}
lca = LCA(ch);
int t = 0;
auto dfs = [&] (auto dfs, int v, int pa) -> void {
dfn[v] = ++t;
for (auto&& [u, w] : e[v]) {
if (u == pa) continue;
ps[u] = ps[v] + w;
dfs(dfs, u, v);
}
};
dfs(dfs, root, 0);
}
// returned vertex number starts from 0
vector<vector<pil>> generate(vector<int> pivots) {
int m = pivots.size();
if (m == 0) return {};
sort_by_key(pivots.begin(), pivots.end(), expr(dfn[v], int v));
vector<int> a;
for (int i = 0; i < m - 1; ++i) {
int v = pivots[i];
int u = lca.query(pivots[i], pivots[i + 1]);
a.emplace_back(v);
a.emplace_back(u);
}
a.emplace_back(pivots[m - 1]);
sort_by_key(a.begin(), a.end(), expr(dfn[v], int v));
m = unique(a.begin(), a.end()) - a.begin();
unordered_map<int, int, safe_hash> mp;
for (int i = 0; i < m; ++i) {
mp[a[i]] = i;
}
vector<vector<pil>> ret(m);
for (int i = 0; i < m - 1; ++i) {
int l = lca.query(a[i], a[i + 1]);
edgew(ret, mp[l], i + 1, ps[a[i + 1]] - ps[l]);
}
return ret;
}
};