#include <bits/stdc++.h>
using namespace std;
using LL = long long;
const int MOD = 998244353;
int f[1002][1000];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  vector<int> x(n);
  for (int i = 0; i < n; ++i) cin >> x[i];
  sort(x.begin(), x.end());
  int ans = 0;
  for (int t = 1; t <= (x[n - 1] - x[0]) / (k - 1); ++t) {
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < k; ++j) f[i][j] = 0;
    }
    f[0][0] = 1;
    int pre = -1;
    for (int i = 1; i < n; ++i) {
      while (x[pre + 1] <= x[i] - t) ++pre;
      f[i][0] = i + 1;
      if (pre == -1) continue;
      for (int j = 1; j < k; ++j) {
        f[i][j] = f[i - 1][j] + f[pre][j - 1];
        if (f[i][j] >= MOD) f[i][j] -= MOD;
      }
    }
    ans += f[n - 1][k - 1];
    if (ans >= MOD) ans -= MOD;
  }
  cout << ans << endl;
  return 0;
}
