#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
const int MOD = 998244353;
int n, k;
int ans;
int v[1005], dp[1005][1005], sp[1005][1005];
void add(int &a, int b) {
  a += b;
  if (a >= MOD) a -= MOD;
}
int solve(int val) {
  int l = 1;
  for (int i = 1; i <= n; i++) {
    dp[i][1] = 1;
    sp[i][1] = sp[i - 1][1] + 1;
    while (v[l] + val <= v[i]) l++;
    if (v[l] + val > v[i]) l = max(l - 1, 0);
    for (int j = 2; j <= min(i, k); j++) {
      dp[i][j] = sp[l][j - 1];
      sp[i][j] = sp[i - 1][j];
      add(sp[i][j], dp[i][j]);
    }
  }
  int ans = 0;
  for (int i = k; i <= n; i++) add(ans, dp[i][k]);
  return ans;
}
int main() {
  ios_base ::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> k;
  for (int i = 1; i <= n; i++) cin >> v[i];
  sort(v + 1, v + n + 1);
  for (int val = 1; val <= v[n] / (k - 1); val++)
    ans = (ans + solve(val)) % MOD;
  cout << ans;
  return 0;
}
