#include <bits/stdc++.h>
using namespace std;
const int Maxn = 2e5 + 10;
long long Inf = 1e18;
const int Log = 20;
const long long Sqrt = 1000000;
const long long Mod = 998244353LL;
long long mul(long long a, long long b) {
  a %= Mod;
  b %= Mod;
  return (a * b) % Mod;
}
long long bin_pow(long long b, long long p) {
  long long res = 1;
  for (long long j = 1, pw = b; j <= p; j <<= 1, pw = mul(pw, pw))
    if (p & j) res = mul(res, pw);
  return res;
}
long long a[Maxn];
long long X = 110000;
long long cnt[Maxn];
long long dp[1010][1010];
long long ps[1010][1010];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, k;
  cin >> n >> k;
  for (int i = 1; i <= n; i++) cin >> a[i];
  a[0] = -10000000;
  sort(a + 1, a + n + 1);
  long long mx = X / max(1LL, (k - 1));
  for (int i = 1; i <= mx; i++) {
    for (int ii = 1; ii <= n; ii++)
      for (int j = 1; j <= k; j++) dp[ii][j] = 0, ps[ii][j] = 0;
    long long p1 = 0;
    dp[0][0] = 1;
    ps[0][0] = 1;
    for (int j = 1; j <= n; j++) ps[j][0] = 1;
    for (int j = 1; j <= n; j++) {
      while (a[p1] + i <= a[j]) {
        p1++;
      }
      p1--;
      for (int K = 1; K <= k; K++) {
        dp[j][K] = ps[p1][K - 1];
        ps[j][K] = (ps[j - 1][K] + dp[j][K]) % Mod;
      }
      cnt[i] += dp[j][k];
      cnt[i] %= Mod;
    }
  }
  long long ans = 0;
  for (int i = 1; i <= mx; i++) {
    ans += mul(i, cnt[i] - cnt[i + 1]);
    ans %= Mod;
  }
  ans += Mod;
  cout << ans % Mod;
  return 0;
}
