#include <bits/stdc++.h>
using namespace std;
const long long maxx = 100000 + 7;
const long long maxn = 1000 + 7;
const long long mod = 998244353;
const long long maxs = 5 * (1E5) + 7;
const long long maxm = 30000 + 7;
const long long maxk = 800 + 7;
const long long maxw = 100 + 7;
const long long maxh = 100 + 7;
const double inf = 1e18 + 7;
ostream& operator<<(ostream& os, pair<long long, long long>& rhs) {
  os << rhs.first << " " << rhs.second << endl;
  return os;
}
long long seq[maxn];
long long dp[maxn][maxn];
long long n, k;
long long ans[maxx];
long long lim;
void init() {
  scanf("%lld%lld", &n, &k);
  for (long long i = (1); i <= (n); i++) scanf("%lld", &seq[i]);
  sort(seq + 1, seq + n + 1);
  lim = (seq[n] / (k - 1) + 1);
}
void solve() {
  long long xs = 0;
  for (long long x = (0); x <= (lim); x++) {
    long long p = 1;
    for (long long i = (2); i <= (n); i++) {
      while (p < i && seq[i] - seq[p] >= x) p++;
      dp[i][2] = dp[i - 1][2] + p - 1;
      for (long long j = (3); j <= (min(k, i)); j++)
        dp[i][j] = (dp[i - 1][j] + dp[p - 1][j - 1]) % mod;
    }
    ans[x] = dp[n][k];
    if (x) {
      long long tmp = (ans[x - 1] - ans[x] + mod) % mod;
      long long tt = tmp * (x - 1) % mod;
      xs += tt;
      xs %= mod;
    }
  }
  printf("%lld\n", xs);
}
int main(void) {
  init();
  solve();
  return 0;
}
