#include <bits/stdc++.h>
using namespace std;
long long f[1011][1011], ans[100011], g[1011], a[1011], n = 0, s = 0,
                                                        allans = 0;
signed main() {
  register long long i = 0, j = 0, k = 0, p = 0;
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> s;
  for (i = 1; i <= n; ++i) {
    cin >> a[i];
  }
  sort(a + 1, a + n + 1);
  a[0] = -0x3f3f3f3f;
  for (i = a[n] / (s - 1); i; --i) {
    for (j = 0; j <= n; ++j) {
      f[0][j] = 1;
    }
    for (j = 1; j <= s; ++j) {
      for (p = j - 1, k = j; k <= n; ++k) {
        for (; p <= k && a[k] - a[p] >= i; ++p)
          ;
        if (j >= 2) {
          f[j][k] =
              (f[j][k - 1] + f[j - 1][p - 1] + 998244353 - f[j - 1][j - 2]) %
              998244353;
        } else {
          f[j][k] = f[j][k - 1] + f[j - 1][p - 1];
        }
      }
    }
    allans = (allans + f[s][n]) % 998244353;
  }
  cout << allans << endl;
  return 0;
}
