Code mẫu

#include <bits/stdc++.h>
using namespace std;

const int N = 505, K = 505, MOD = 1E9 + 7;

int n, k, a[N], dp[N][K];
long long ans = 0;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    freopen("DIARR.inp", "r", stdin);
    freopen("DIARR.out", "w", stdout);
    cin >> n >> k;
    if (k == 1) {
        return cout << 0, 0;
    }
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    sort(a + 1, a + n + 1);
    dp[0][0] = 1;
    for (int mi = 1; mi <= a[n] / (k - 1); mi++) {
        for (int i = 1, pt = 1; i <= n; i++) {
            fill(dp[i], dp[i] + k + 1, 0);
            for (; pt < i && a[i] - a[pt] >= mi; pt++);
            for (int j = 1; j <= k; j++) {
                (dp[i][j] += dp[pt - 1][j - 1]) %= MOD;
            }
            for (int j = 0; j <= k; j++) {
                (dp[i][j] += dp[i - 1][j]) %= MOD;
            }
        }
        (ans += dp[n][k]) %= MOD;
    }
    cout << ans;
}