#include <bits/stdc++.h>
using namespace std;
int n, K, w[1010], S[1010][1010], Mod = 998244353;
int Z[101000];
int Calc(int KK) {
  int i, j;
  int prev = 0;
  for (i = 1; i <= n; i++) {
    while (prev + 1 < i && w[prev + 1] + KK <= w[i]) prev++;
    for (j = 1; j <= K; j++) {
      S[i][j] = S[i - 1][j];
    }
    S[i][1] = (S[i][1] + 1) % Mod;
    for (j = 2; j <= K; j++) {
      S[i][j] = (S[i][j] + S[prev][j - 1]) % Mod;
    }
  }
  return S[n][K];
}
int main() {
  int i;
  scanf("%d%d", &n, &K);
  for (i = 1; i <= n; i++) {
    scanf("%d", &w[i]);
  }
  sort(w + 1, w + n + 1);
  for (i = 0; i <= 100000 / (K - 1); i++) {
    Z[i] = Calc(i);
  }
  long long res = 0;
  for (i = 0; i <= 100000 / (K - 1); i++) {
    Z[i] = Z[i] - Z[i + 1];
    res = (res + 1ll * Z[i] * i) % Mod;
  }
  printf("%lld\n", res);
}
