163 lines
3.1 KiB
C++
163 lines
3.1 KiB
C++
/* Problem URL: https://codeforces.com/problemset/problem/1781/D */
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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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int n;
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cin >> n;
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vl a(n);
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cin >> a;
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set<ll> cand;
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auto getcand = [&](ll a, ll b) {
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ll diff = b - a;
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for (ll i = 1; i * i <= diff; i++) {
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if (diff % i == 0) {
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ll p2 = (diff / i - i);
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ll q2 = (diff / i + i);
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if (p2 < 0 || q2 < 0 || (p2 & 1) || (q2 & 1)) {
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continue;
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}
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p2 >>= 1;
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q2 >>= 1;
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cand.insert(p2 * p2 - a);
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cand.insert(q2 * q2 - b);
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}
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}
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};
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rep(i, n - 1) {
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nrep(j, i + 1, n) {
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getcand(a[i], a[j]);
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}
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}
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cand.insert(0);
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auto issquare = [&](ll a) {
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ll lim = sqrtl(a);
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return lim * lim == a;
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};
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int ans = 1;
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repv(now, cand) {
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if (now < 0) {
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continue;
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}
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int cur = 0;
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rep(j, n) {
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if (issquare(a[j] + now)) {
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cur++;
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}
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}
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rmax(ans, cur);
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}
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cout << ans << '\n';
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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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