#include <bits/stdc++.h>
using namespace std;
long long ans;
long long n;
long long k;
long long a[1005];
long long f[1005][1005];
long long s[1005][1005];
int main() {
  scanf("%lld %lld", &n, &k);
  for (long long i = 1; i <= n; ++i) scanf("%lld", a + i);
  sort(a + 1, a + 1 + n);
  s[0][0] = 1LL;
  for (long long gap = 1; gap * (k - 1) <= a[n] - a[1]; ++gap) {
    long long pre = 0;
    for (long long i = 1; i <= n; ++i) {
      while (a[i] - a[pre + 1] >= gap) ++pre;
      f[i][1] = 1LL;
      s[i][1] = (s[i - 1][1] + f[i][1]) % 998244353;
      for (long long j = 2; j <= min(i, k); ++j) {
        f[i][j] = s[pre][j - 1];
        s[i][j] = (s[i - 1][j] + f[i][j]) % 998244353;
      }
    }
    ans = (ans + s[n][k]) % 998244353;
  }
  printf("%lld\n", ans);
  return 0;
}
