#include <bits/stdc++.h>
using namespace std;
int a[1005], dp[1005][1005], dp_sum[1005][1005];
int main() {
  ios::sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  for (int i = 1; i <= n; i++) cin >> a[i];
  sort(a + 1, a + n + 1);
  int limit = a[n] / (k - 1);
  int ans = 0;
  for (int diff = 1; diff <= limit; diff++) {
    for (int j = 1; j <= n; j++) dp_sum[j][1] = j, dp[j][1] = 1;
    for (int ct = 2; ct <= k; ct++) {
      for (int j = 1, l = 1; j <= n; j++) {
        while (l < j && a[j] - a[l] >= diff) l++;
        dp[j][ct] = dp_sum[l - 1][ct - 1];
        dp_sum[j][ct] = dp[j][ct] + dp_sum[j - 1][ct];
        if (dp_sum[j][ct] >= 998244353) dp_sum[j][ct] -= 998244353;
      }
    }
    ans += dp_sum[n][k];
    if (ans >= 998244353) ans -= 998244353;
  }
  cout << ans << endl;
}
