44 lines
1.4 KiB
C++
44 lines
1.4 KiB
C++
namespace HLD {
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struct node_info {
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int father, depth, hson, size, head, dfn = -1;
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};
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// returns: (dfs sequence, node info)
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// node numbering starts from `1`
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// if `dfn(v) == -1`, then node `v` is never accessed.
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pair<vector<int>, vector<node_info>> work(const vector<vector<int>>& ch, int root = 0) {
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int n = ch.size() - 1;
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vector<int> seq;
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vector<node_info> res(n + 1);
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auto dfs1 = [&] (auto dfs1, int v, int pa) -> void {
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res[v].father = pa;
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res[v].depth = res[pa].depth + 1;
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res[v].size = 1;
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int mx = 0;
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for (auto&& u : ch[v]) {
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if (u == pa) continue;
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dfs1(dfs1, u, v);
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res[v].size += res[u].size;
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if (res[u].size > mx) {
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mx = res[u].size;
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res[v].hson = u;
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}
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}
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};
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dfs1(dfs1, root, root);
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int tm = 0;
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auto dfs2 = [&] (auto dfs2, int v, int head) -> void {
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res[v].dfn = tm++;
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seq.emplace_back(v);
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res[v].head = head;
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if (not res[v].hson) return;
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dfs2(dfs2, res[v].hson, head);
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for (auto&& u : ch[v]) {
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if (u == res[v].father or u == res[v].hson) continue;
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dfs2(dfs2, u, u);
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}
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};
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dfs2(dfs2, root, root);
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return { seq, res };
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}
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}
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