150 lines
2.8 KiB
C++
150 lines
2.8 KiB
C++
/* Problem URL: https://cses.fi/problemset/task/1693 */
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#include <bits/stdc++.h>
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#include <ext/pb_ds/assoc_container.hpp>
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#include <ext/pb_ds/tree_policy.hpp>
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using namespace std;
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using namespace __gnu_pbds;
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template <class T, class comp = less<>>
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using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
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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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vi out(n);
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vi in(n);
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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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out[a]++;
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in[b]++;
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graph[a].push_back(b);
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}
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auto check = [&]() {
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if (out[0] != in[0] + 1 || out[n - 1] + 1 != in[n - 1]) {
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return false;
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};
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nrep(i, 1, n - 1) {
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if (out[i] != in[i]) {
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return false;
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}
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}
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return true;
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};
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if (!check()) {
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cout << "IMPOSSIBLE\n";
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return 0;
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}
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stack<int> s;
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s.push(0);
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vi path;
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while (!s.empty()) {
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int i = s.top();
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if (graph[i].empty()) {
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path.push_back(i + 1);
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s.pop();
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continue;
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}
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s.push(graph[i].back());
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graph[i].pop_back();
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}
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rep(i, n) {
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if (!graph[i].empty()) {
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cout << "IMPOSSIBLE\n";
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return 0;
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}
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}
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reverse(all(path));
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cout << path;
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}
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