161 lines
3.0 KiB
C++
161 lines
3.0 KiB
C++
/* Problem URL: https://codeforces.com/contest/2120/problem/C */
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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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const int oo = INT32_MAX >> 1;
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const ll OO = INT64_MAX >> 1;
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void pre()
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{
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}
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#define TEST 1
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void solve()
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{
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ll n, m;
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cin >> n >> m;
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ll high = n * (n + 1) / 2;
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if (m < n || m > high) {
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cout << "-1\n";
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return;
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}
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set<ll, greater<>> all;
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nrep(i, 1, n + 1) {
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all.insert(i);
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}
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V<pair<int, int>> edges;
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int root = -1;
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int prev = -1;
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auto itr = all.begin();
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while (n < m) {
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while (n - 1 > m - *itr) {
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itr++;
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}
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n--;
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m -= *itr;
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if (root == -1) {
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root = *itr;
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prev = root;
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itr = all.erase(itr);
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continue;
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}
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edges.emplace_back(prev, *itr);
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prev = *itr;
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itr = all.erase(itr);
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}
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if (prev == -1) {
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root = 1;
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} else {
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edges.emplace_back(prev, 1);
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}
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all.erase(1);
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itr = all.begin();
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while (itr != all.end()) {
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edges.emplace_back(1, *itr);
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itr++;
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}
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cout << root << '\n';
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repv(i, edges) {
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cout << i.first << ' ' << i.second << '\n';
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}
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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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pre();
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int t;
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(TEST && cin >> t) || (t = 1);
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while (t--) {
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solve();
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}
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}
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