#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1010;
const int MAXK = 1010;
const int MAXB = 100010;
const int MOD = 998244353;
int a[MAXN];
int dp[MAXN][MAXK];
int gb[MAXB];
int psum[MAXN][MAXK];
int main() {
  int n, k;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  int maxb = min(MAXB - 1, MAXB / (k - 1) + 1);
  for (int b = 0; b <= maxb; b++) {
    for (int i = 0; i < n; i++)
      for (int j = 0; j <= k; j++) {
        dp[i][j] = 0;
        psum[i][j] = 0;
      }
    for (int i = 0; i < n; i++) {
      dp[i][1] = 1;
      psum[i][1] = i + 1;
    }
    int prvi = -1;
    for (int i = 1; i < n; i++) {
      while (prvi < i - 1 && a[prvi + 1] <= a[i] - b) {
        prvi += 1;
      }
      for (int j = 2; j <= k; j++) {
        if (prvi == -1) {
          dp[i][j] = 0;
        } else {
          dp[i][j] = psum[prvi][j - 1];
        }
        psum[i][j] = psum[i - 1][j] + dp[i][j];
        psum[i][j] %= MOD;
      }
    }
    gb[b] = 0;
    for (int i = 0; i < n; i++) {
      gb[b] += dp[i][k];
      gb[b] %= MOD;
    }
  }
  int res = 0;
  for (int b = 0; b < maxb; b++) {
    int t = ((long long)b * ((long long)gb[b] - gb[b + 1])) % MOD + MOD;
    t %= MOD;
    res += t;
    res = res % MOD;
  }
  cout << res << endl;
}
