#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)2e9;
const long long md = 1000000007;
long long dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1};
long long power(long long a, long long p, long long md) {
  long long ans = 1;
  while (p) {
    if (p & 1) ans *= a;
    p /= 2;
    a *= a;
    ans %= md;
    a %= md;
  }
  return ans;
}
long long mdinv(long long a) { return power(a, md - 2, md); }
long long arr[1003];
long long n, k;
long long DP[1003][1003];
long long last[1003];
signed main() {
  const long long mm = 998244353;
  cin >> n >> k;
  for (long long i = 0; i < (long long)n; i++) cin >> arr[i];
  sort(arr, arr + n);
  long long ans = 0;
  for (long long diff = 1; diff <= (arr[n - 1]) / (k - 1) + 2; diff++) {
    long long first = 0, second = 0;
    for (; second < n; second++) {
      while (arr[second] - arr[first] >= diff) first++;
      last[second] = first - 1;
    }
    for (long long i = 0; i < (long long)1003; i++) DP[0][i] = 0;
    DP[0][1] = 1;
    for (long long i = 1; i < n; i++) {
      DP[i][1] = i + 1;
      for (long long len = 2; len <= k; len++) {
        DP[i][len] = DP[i - 1][len];
        if (last[i] >= 0) DP[i][len] += DP[last[i]][len - 1];
        DP[i][len] %= mm;
      }
    }
    ans += DP[n - 1][k];
    ans %= mm;
  }
  cout << ans;
}
