143 lines
2.8 KiB
C++
143 lines
2.8 KiB
C++
/* Problem URL: https://cses.fi/problemset/task/1669 */
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#include <bits/stdc++.h>
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using namespace std;
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#define V vector
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#define rmin(a, b) a = min(a, b)
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#define rmax(a, b) a = max(a, b)
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#define rep(i, lim) for (int i = 0; i < (lim); i++)
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#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
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#define repv(i, v) for (auto &i : (v))
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#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
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#define sortv(v) sort(v.begin(), v.end())
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#define all(v) (v).begin(), (v).end()
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using vi = vector<int>;
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using vvi = vector<vi>;
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using vvvi = vector<vvi>;
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using vvvvi = vector<vvvi>;
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using ll = long long;
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using vl = vector<ll>;
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using vvl = vector<vl>;
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using vvvl = vector<vvl>;
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using vvvvl = vector<vvvl>;
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template<class v>
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auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
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os << vec[0];
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for (size_t i = 1; i < vec.size(); i++) {
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os << ' ' << vec[i];
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}
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os << '\n';
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<v> &vec)->istream& {
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for (auto &i : vec) {
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is >> i;
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}
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return is;
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}
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template<class v>
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auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
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for (auto &i : vec) {
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os << i[0];
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for (size_t j = 1; j < i.size(); j++) {
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os << ' ' << i[j];
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}
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os << '\n';
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}
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<vector<v>> &vec)->istream& {
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for (auto &i : vec) {
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for (auto &j : i) {
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is >> j;
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}
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}
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return is;
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(nullptr);
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int n, m;
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cin >> n >> m;
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vvi graph(n);
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while (m--) {
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int a, b;
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cin >> a >> b;
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a--, b--;
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graph[a].push_back(b);
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graph[b].push_back(a);
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}
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vi parent(n, -1);
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V<bool> frame(n, false);
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vi ans;
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function<bool(int, int)> dfs = [&](int i, int p) {
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frame[i] = true;
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repv(j, graph[i]) {
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if (frame[j] && j != p) {
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ans.push_back(i + 1);
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int p = parent[i];
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while (p != j) {
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ans.push_back(p + 1);
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p = parent[p];
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}
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ans.push_back(j + 1);
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ans.push_back(i + 1);
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return true;
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}
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if (parent[j] != -1) {
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continue;
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}
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parent[j] = i;
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if (dfs(j, i)) {
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return true;
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}
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}
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frame[i] = false;
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return false;
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};
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rep(i, n) {
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if (parent[i] != -1) {
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continue;
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}
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if (dfs(i, i)) {
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break;
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}
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}
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if (ans.empty()) {
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cout << "IMPOSSIBLE\n";
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return 0;
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}
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cout << ans.size() << '\n' << ans;
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}
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