An Animal Contest 2 P2 - Koala Party

    1#include <bits/stdc++.h>
    2using namespace std;
    3using ll = long long;
    4using i128 = __int128;
    5const int inf = 1e9;
    6const ll INF = 1LL << 60; //❄️
    7int main() {
    8    ios::sync_with_stdio(0); cin.tie(0); 
    9    int n; cin >> n;
    10    if (n == 2) {
    11        int s = 0;
    12        for (int i = 0; i < n; i++) {
    13            int x; cin >> x;
    14            s += x;
    15        }
    16        cout << (s & 1 ? 1 : 2) << '\n';
    17    } else {
    18        vector<int> v(n);
    19        for (int i = 0; i < n; i++) cin >> v[i];
    20        sort(v.begin(), v.end());
    21        for (int i = 1; i < n - 1; i++) {
    22            int l = i - 1, r = i + 1;
    23            while (l >= 0 && r < v.size()) {
    24                ll s = v[l] + v[r];
    25                ll mid = 2LL * v[i];
    26                if (s == mid) {
    27                    cout << 3 << '\n';
    28                    return 0;
    29                } else if (s < mid) {
    30                    r++;
    31                } else {
    32                    l--;
    33                }
    34            }
    35        }
    36        cout << 2 << '\n';
    37    }
    38    return 0;
    39}