Language: C++

#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#define ms(s, n) memset(s, n, sizeof(s))
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORd(i, a, b) for (int i = (a) - 1; i >= (b); --i)
#define FORall(it, a) for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define sz(a) int((a).size())
#define present(t, x) (t.find(x) != t.end())
#define all(a) (a).begin(), (a).end()
#define uni(a) (a).erase(unique(all(a)), (a).end())
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define prec(n) fixed<<setprecision(n)
#define bit(n, i) (((n) >> (i)) & 1)
#define bitcount(n) __builtin_popcountll(n)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vii;
const int MOD = (int) 1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int) 1e9 + 23111992;
const ll LINF = (ll) 1e18 + 23111992;
const ld PI = acos((ld) -1);
const ld EPS = 1e-9;
inline ll gcd(ll a, ll b) {ll r; while (b) {r = a % b; a = b; b = r;} return a;}
inline ll lcm(ll a, ll b) {return a / gcd(a, b) * b;}
inline ll fpow(ll n, ll k, int p = MOD) {ll r = 1; for (; k; k >>= 1) {if (k & 1) r = r * n % p; n = n * n % p;} return r;}
template<class T> inline int chkmin(T& a, const T& val) {return val < a ? a = val, 1 : 0;}
template<class T> inline int chkmax(T& a, const T& val) {return a < val ? a = val, 1 : 0;}
inline ull isqrt(ull k) {ull r = sqrt(k) + 1; while (r * r > k) r--; return r;}
inline ll icbrt(ll k) {ll r = cbrt(k) + 1; while (r * r * r > k) r--; return r;}
inline void addmod(int& a, int val, int p = MOD) {if ((a = (a + val)) >= p) a -= p;}
inline void submod(int& a, int val, int p = MOD) {if ((a = (a - val)) < 0) a += p;}
inline int mult(int a, int b, int p = MOD) {return (ll) a * b % p;}
inline int inv(int a, int p = MOD) {return fpow(a, p - 2, p);}
inline int sign(ld x) {return x < -EPS ? -1 : x > +EPS;}
inline int sign(ld x, ld y) {return sign(x - y);}
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int mrand() {return abs((int) mt());}
inline int mrand(int k) {return abs((int) mt()) % k;}
#define db(x) cerr << "[" << #x << ": " << (x) << "] ";
#define endln cerr << "\n";

struct frac_t {
    long long p, q;
    frac_t(long long p = 0, long long q = 1) : p(p), q(q) {}
    friend int operator < (frac_t a, frac_t b) {
        a.normalize(), b.normalize();
        return (__int128) a.p * b.q < (__int128) b.p * a.q;
    }
    void normalize() {
        if (q < 0) {
            p *= -1, q *= -1;
        }
        long long g = __gcd(abs(p), q);
        p /= g, q /= g;
    }
    frac_t operator + (frac_t rhs) {
        frac_t res(p * rhs.q + rhs.p * q, q * rhs.q);
        res.normalize();
        return res;
    }
    frac_t operator - (frac_t rhs) {
        frac_t res(p * rhs.q - rhs.p * q, q * rhs.q);
        res.normalize();
        return res;
    }
    frac_t operator * (frac_t rhs) {
        frac_t res(p * rhs.p, q * rhs.q);
        res.normalize();
        return res;
    }
};

void chemthan() {
#define double long double
    int n; cin >> n;
    vector<long long> a(n);
    vector<long long> b(n);
    FOR(i, 0, n) cin >> a[i];
    FOR(i, 0, n) cin >> b[i];
    map<long long, vi> hs;
    FOR(i, 0, n) hs[-a[i]].pb(i + n);
    int nn = n + n + n;
    vector<vector<long long>> st(2, vector<long long>(nn << 1));
    auto upd = [&] (vector<long long>& st, int p, long long v) {
        for (st[p += nn] = v; 1 < p; ) p >>= 1, st[p] = st[p << 1] + st[p << 1 | 1];
    };
    auto query = [&] (vector<long long>& st, int l, int r) {
        long long res = 0;
        for (l += nn, r += nn + 1; l < r; l >>= 1, r >>= 1) {
            if (l & 1) res += st[l++];
            if (r & 1) res += st[--r];
        }
        return res;
    };
    FOR(i, 0, n) {
        upd(st[0], i, b[i]);
        upd(st[1], i, b[i] * i);
        upd(st[0], i + n, b[i]);
        upd(st[1], i + n, b[i] * (i + n));
        upd(st[0], i + n + n, b[i]);
        upd(st[1], i + n + n, b[i] * (i + n + n));
    }
    vector<frac_t> dp(n);
    set<int> ss;
    for (auto e : hs) {
        if (!sz(ss)) {
            for (int i : e.se) {
                dp[i % n] = frac{a[i % n], 1};
            }
        }
        else {
            for (int i : e.se) {
                auto it = ss.lower_bound(i);
                int q = *it;
                int p = *(--it);
                frac_t sum;
                long long x = query(st[0], p + 1, i);
                long long y = query(st[1], p + 1, i);
                sum.p -= (y - p * x) * 2 * (q - i);
                x = query(st[0], i + 1, q - 1);
                y = query(st[1], i + 1, q - 1);
                sum.p -= (q * x - y) * 2 * (i - p);
                sum.q = q - p;
                sum = sum + frac_t(q - i, q - p) * dp[p % n];
                sum = sum + frac_t(i - p, q - p) * dp[q % n];
                chkmax(sum, frac_t(a[i % n], 1));
                dp[i % n] = sum;
            }
        }
        for (int i : e.se) {
            ss.insert(i - n);
            ss.insert(i);
            ss.insert(i + n);
        }
    }
    double res = 0;
    FOR(i, 0, n) res += (double) dp[i].p / dp[i].q / n;
    cout << prec(12) << res << "\n";
}

int main(int argc, char* argv[]) {
    ios_base::sync_with_stdio(0), cin.tie(0);
    if (argc > 1) {
        assert(freopen(argv[1], "r", stdin));
    }
    if (argc > 2) {
        assert(freopen(argv[2], "wb", stdout));
    }
    chemthan();
    cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
    return 0;
}


Compiler output:
a.cc: In function 'void chemthan()':
a.cc:119:29: error: 'frac' was not declared in this scope
  119 |                 dp[i % n] = frac{a[i % n], 1};
      |                             ^~~~