#include <bits/stdc++.h>
using namespace std;
int k, n;
const int maxn = 1e3 + 10;
const int mod = 998244353;
int a[maxn];
int dp[maxn][maxn];
int solve(int limit) {
  for (int i = 1; i <= n; ++i) dp[i][1] = 1;
  for (int j = 2; j <= k; ++j) {
    int now_v = 0, now_i = j - 2;
    for (int i = j; i <= n; ++i) {
      while (a[now_i + 1] + limit <= a[i] && now_i + 1 < i) {
        now_i++;
        now_v = (now_v + dp[now_i][j - 1]) % mod;
      }
      dp[i][j] = now_v;
    }
  }
  int ans = 0;
  for (int i = k; i <= n; ++i) ans = (ans + dp[i][k]) % mod;
  return ans;
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  sort(a + 1, a + 1 + n);
  int ans = 0;
  for (int i = 1; i <= (a[n] - a[1]) / (k - 1); ++i)
    ans = (ans + solve(i)) % mod;
  cout << ans << endl;
  return 0;
}
