#include <bits/stdc++.h>
#define range(i, l, r) for(long long int (i) = (l); (i) < (r); (i)++)
#define reversed_range(i, l, r) for (long long int (i) = (r) - 1; (i) >= l; (i)--)
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;

template <typename S, typename T>
ostream& operator <<(ostream& os, pair<S, T> p) {
    os << "(";
    os << p.first << ", " << p.second;
    return os << ")";
}

template <typename T>
ostream& operator <<(ostream& os, vec<T> v) {
    os << "[";
    if (v.size() == 0) return os << "]";
    for (int i = 0; i < v.size() - 1; i++) {
        os << v.at(i) << ", ";
    }
    return os << v.at(v.size() - 1) << "]";
}

template <typename T>
ostream& operator <<(ostream& os, set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    os << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        os << ", " << *it;
    }
    return os << "}";
}

template <typename T>
ostream& operator <<(ostream& os, unordered_set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    os << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        os << ", " << *it;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    os << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        os << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, unordered_map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    os << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        os << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

lint pow(lint num, lint e, lint MOD) {
    lint res = 1;
    lint cur_num = num;
    while (e) {
        if (e & 1) {
            res *= cur_num;
            res %= MOD;
        }
        cur_num *= cur_num;
        cur_num %= MOD;
        e >>= 1;
    }
    return res;
}

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    const lint MOD = 1e9 + 7;
    lint N, K; cin >> N >> K;
    vec<lint> A_list(N);
    range(i, 0, N) cin >> A_list.at(i);
    map<lint, lint> num_occurances;
    range(i, 0, N) num_occurances[A_list.at(i)] += 1;
    unordered_map<lint, lint> num_smaller;
    lint cur_num = 0;
    for (const auto& p : num_occurances) {
        num_smaller[p.first] = cur_num;
        cur_num += p.second;
    }
    vec<lint> factorial(N + 1), inv_factorial(N + 1);
    factorial.at(0) = 1; inv_factorial.at(0) = 1;
    range(i, 1, N + 1) {
        factorial.at(i) = factorial.at(i - 1) * i % MOD;
        inv_factorial.at(i) = pow(factorial.at(i), MOD - 2, MOD);
    }
    // cout << factorial << "\n";
    // cout << inv_factorial << "\n";
    auto comb = [&](lint n, lint m) {
        return factorial.at(n) * inv_factorial.at(m) % MOD * inv_factorial.at(n - m) % MOD;
    };
    lint ans = 0;
    // cout << num_occurances << "\n";
    // cout << num_smaller << "\n";
    for (const auto& p : num_occurances) {
        lint n_smaller = num_smaller.at(p.first);
        lint n_same = p.second;
        lint n_larger = N - n_smaller - n_same;
        lint n_occurances_as_max = (n_smaller + n_same >= K ? comb(n_smaller + n_same, K) : 0) - (n_smaller >= K ? comb(n_smaller, K) : 0);
        lint n_occurances_as_min = (n_same + n_larger >= K ? comb(n_same + n_larger, K) : 0) - (n_larger >= K ? comb(n_larger, K) : 0);
        ans += p.first * (n_occurances_as_max - n_occurances_as_min);
        ans %= MOD;
        // ans += p.first * ((n_smaller + n_same >= K) ? comb(n_smaller + n_same - 1, K - 1) : 0);
        // ans %= MOD;
        // ans -= p.first * ((n_same + n_larger >= K) ? comb(n_same + n_larger - 1, K - 1) : 0);
        // ans %= MOD;
        if (ans < 0) ans += MOD;
        // cout << n_smaller << " " << n_same << " " << n_larger << "\n";
        // cout << n_occurances_as_max << " " << n_occurances_as_min << "\n";
        // cout << ans << "\n";
    }
    cout << ans << "\n";
}

Measured memory_bytes: 12196