Language: C++

#include <bits/stdc++.h>
#include <boost/range.hpp>
#include <boost/range/algorithm.hpp>
#include <boost/range/algorithm_ext.hpp>
#include <boost/range/numeric.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/irange.hpp>
using namespace std;
constexpr char nl = '\n';
using ll = long long;
using boost::irange;
namespace rng {
    using namespace boost;
    using namespace boost::range;
    using namespace boost::adaptors;
}

struct init_ { init_(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); } } init_;

template<class C> auto operator>>(istream& in, C& c) -> typename enable_if<!is_void<decltype(c.begin())>::value && !is_same<C, string>::value, istream&>::type {
    for (auto& v : c) { in >> v; } return in; }
template<class C> auto operator<<(ostream& out, const C& c) -> typename enable_if<!is_void<decltype(c.begin())>::value && !is_same<C, string>::value, ostream&>::type {
    int i = 0; for (const auto& v : c) { if (i++) { out << ' '; } out << v; } return out; }
template<size_t N, class T, class R> using when_last = typename enable_if<N == tuple_size<remove_reference_t<T>>::value - 1, R>::type;
template<size_t N, class T, class R> using when_init = typename enable_if<N != tuple_size<remove_reference_t<T>>::value - 1, R>::type;
template<size_t N = 0, class T> auto operator>>(istream& in, T&& t) -> when_last<N, T, istream&> { return in >> get<N>(t); }
template<size_t N = 0, class T> auto operator>>(istream& in, T&& t) -> when_init<N, T, istream&> { return operator>><N + 1>(in >> get<N>(t), forward<T>(t)); }
template<size_t N = 0, class T> auto operator<<(ostream& out, const T& t) -> when_last<N, T, ostream&> { return out << get<N>(t); }
template<size_t N = 0, class T> auto operator<<(ostream& out, const T& t) -> when_init<N, T, ostream&> { return operator<<<N + 1>(out << get<N>(t) << ' ', t); }

#ifdef LOCAL
constexpr auto color_s_ = "\033[2m\033[33m", color_e_ = "\033[0m";
template<class T> void trace_(const T& v) { cerr << v; }
template<class T> void trace_(const vector<vector<T>>& m) { cerr << "\n"; for (const auto& v : m) { trace_(v); cerr << "\n"; } }
template<class T> void trace_(const char* s, const T& v) { cerr << color_s_ << s << "="; trace_(v); cerr << color_e_ << "\n"; cerr.flush(); }
template<class T, class... Ts> void trace_(const char* s, const T& v, const Ts&... vs) { cerr << color_s_; for (; *s != ','; ++s) { cerr << *s; } cerr << "="; trace_(v); cerr << ","; trace_(++s, vs...); }
#define TRACE(...) trace_(#__VA_ARGS__, __VA_ARGS__)
#else
#define TRACE(...)
#endif

constexpr ll mod = 1000000007;

int main() {
    int n;
    ll k;
    cin >> n >> k;
    vector<int> a(n);
    cin >> a;
    ll t = 0;
    for (int j : irange(1, n)) {
        for (int i : irange(j)) {
            if (a[i] > a[j]) {
                t++;
            }
        }
    }
    rng::sort(a);
    ll fn1 = 0, lowers = 0;
    for (int i : irange(1, n)) {
        if (a[i-1] < a[i]) {
            lowers = i;
        }
        fn1 = (fn1 + lowers) % mod;
    }
    TRACE(fn1);
    ll ans = ((k * t) % mod + ((k * (k - 1) / 2 % mod) * fn1) % mod) % mod;
    cout << ans << nl;
}


Compiler output:
a.cc:2:10: fatal error: boost/range.hpp: No such file or directory
    2 | #include <boost/range.hpp>
      |          ^~~~~~~~~~~~~~~~~
compilation terminated.