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Add graph/hld.cc 

Signed-off-by: subcrip <contact@subc.rip>
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subcrip 2024-05-13 17:08:53 +08:00
parent acae6f3294
commit 84fbfb21e2
1 changed files with 43 additions and 0 deletions
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namespace HLD {
struct node_info {
int father, depth, hson, size, head, dfn = -1;
};
// returns: (dfs sequence, node info)
// node numbering starts from `1`
// if `dfn(v) == -1`, then node `v` is never accessed.
pair<vector<int>, vector<node_info>> work(int n, const vector<vector<int>>& ch, int root = 0) {
vector<int> seq;
vector<node_info> res(n + 1);
auto dfs1 = [&] (auto dfs1, int v, int pa) -> void {
res[v].father = pa;
res[v].depth = res[pa].depth + 1;
res[v].size = 1;
int mx = 0;
for (auto&& u : ch[v]) {
if (u == pa) continue;
dfs1(dfs1, u, v);
res[v].size += res[u].size;
if (res[u].size > mx) {
mx = res[u].size;
res[v].hson = u;
}
}
};
dfs1(dfs1, root, root);
int tm = 0;
auto dfs2 = [&] (auto dfs2, int v, int head) -> void {
res[v].dfn = tm++;
seq.emplace_back(v);
res[v].head = head;
if (not res[v].hson) return;
dfs2(dfs2, res[v].hson, head);
for (auto&& u : ch[v]) {
if (u == res[v].father or u == res[v].hson) continue;
dfs2(dfs2, u, u);
}
};
dfs2(dfs2, root, root);
return { seq, res };
}
}