64 lines
1.6 KiB
C++
64 lines
1.6 KiB
C++
struct hierholzer {
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struct edge_t {
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int from, to, rev, stale;
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edge_t(int from, int to, int rev, int stale) : from(from), to(to), rev(rev), stale(stale) {}
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};
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int n;
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vector<edge_t> edges;
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vector<vector<int>> ch;
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quick_union qu;
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hierholzer(int n) : n(n), ch(n + 1), qu(n + 1) {}
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void add_edge(int u, int v) {
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int left = edges.size(), right = left + 1;
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edges.emplace_back(u, v, right, false);
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edges.emplace_back(v, u, left, false);
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ch[u].emplace_back(left);
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ch[v].emplace_back(right);
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qu.merge(u, v);
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}
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optional<vector<int>> solve() {
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if (qu.query_size(1) != n) {
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return nullopt;
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}
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int odd = 0;
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int last_odd;
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for (int i = 1; i <= n; ++i) {
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if (ch[i].size() % 2) {
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odd += 1;
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last_odd = i;
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}
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}
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int start;
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if (odd == 0) {
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start = 1;
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} else if (odd == 2) {
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start = last_odd;
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} else {
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return nullopt;
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}
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vector<int> res;
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auto dfs = [&] (auto&& dfs, int v) -> void {
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while (ch[v].size()) {
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int i = ch[v].back();
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ch[v].pop_back();
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if (not edges[i].stale) {
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edges[i].stale = true;
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edges[edges[i].rev].stale = true;
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dfs(dfs, edges[i].to);
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}
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}
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res.emplace_back(v);
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};
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dfs(dfs, start);
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return res;
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}
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};
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