Submission #75815801

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Source Code Expand

#include <bits/stdc++.h>
#define fastio cin.tie(0)->sync_with_stdio(0)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define compress(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define sz(x) (int)(x).size()
using namespace std;
typedef long long ll;

int main() {
    fastio;
    /* for (int s = 1; s <= 10; s++) {
        vector<int> ord(s); iota(all(ord), 1);
        vector<int> cnt(s+1);
        do {
            vector<int> vis(s+1);
            auto solve = [&](auto solve, int idx) {
                if (idx == s) return true;
                vector<int> cand;
                for (int i = 1; i <= s; i++) {
                    if (!vis[i]) {
                        cand.push_back(i);
                    }
                }
                for (auto i : cand) {
                    cnt[i]++; vis[i] = 1;
                    if (ord[idx] == i && solve(solve, idx+1)) return true;
                    vis[i] = 0;
                    for (int j = 1; j <= s; j++) if (vis[j]) cnt[j]++;
                }
                return false;
            };
            solve(solve, 0);
        } while(next_permutation(all(ord)));
        for (int i = 1; i <= s; i++) cout << cnt[i] << " ";
        cout << "\n";
    }
    int sp = 1;
    for (int s = 1; s <= 10; s++) {
        sp *= s;
        int t = (s-1)*(s-2)/2;
        cout << t << " ";
        cout << sp*t/6 + sp << " ";
        cout << sp/2 << "\n";
    } */
    ll N; cin >> N;
    vector<ll> v(N);
    for (auto &i : v) cin >> i;
    sort(rall(v));
    double ans = 0;
    for (ll i = 0; i < N; i++) {
        ans += ((N-1) * (N-2) / 12.0 + 1 + i / 2.0) * v[i];
    }
    cout.precision(6);
    cout << fixed << ans << "\n";
    return 0;
}

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