Do this one problem because someone asked me to.

It was really simple...

CSES Problem Set/Two Sets.cpp

@@ -0,0 +1,125 @@
+/* Problem URL: https://cses.fi/problemset/task/1092 */
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    ll n;
+    cin >> n;
+
+    ll limit = n * (n + 1) / 2;
+    if (limit % 2 != 0) {
+        cout << "NO\n";
+        return 0;
+    }
+
+    limit /= 2;
+
+    V<bool> group(n, false);
+    group.back() = true;
+    ll sum = n;
+
+    for (size_t i = n - 1; i > 0; i--) {
+        if (sum + i <= limit) {
+            sum += i;
+            group[i - 1] = true;
+        }
+    }
+
+    if (sum != limit) {
+        cout << "NO\n";
+        return 0;
+    }
+
+    cout << "YES\n";
+
+    vl g1, g2;
+    for (size_t i = 0; i < n; i++) {
+        if (group[i]) {
+            g1.push_back(i + 1);
+        } else {
+            g2.push_back(i + 1);
+        }
+    }
+
+    cout << g1.size() << '\n';
+    for (auto i : g1) {
+        cout << i << ' ';
+    }
+    cout << '\n';
+    cout << g2.size() << '\n';
+    for (auto i : g2) {
+        cout << i << ' ';
+    }
+    cout << '\n';
+}