#include <bits/stdc++.h>
using namespace std;
const int mod = 998244353;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  int upper_x = a[n - 1] / (k - 1);
  long long ans = 0;
  for (int x = 1; x <= upper_x; x++) {
    long long dp[n][k + 1];
    long long psum[n][k + 1];
    int last[n];
    for (int i = 0; i < n; i++) {
      last[i] = 0;
      dp[i][1] = 1;
      psum[i][1] = i + 1;
      for (int j = 2; j <= k; j++) {
        dp[i][j] = 0;
        psum[i][j] = 0;
      }
    }
    for (int i = 1; i < n; i++) {
      if (a[i] >= a[i - 1] + x)
        last[i] = i - 1;
      else {
        last[i] = max(last[i - 1], 0);
        while (a[last[i]] + x <= a[i]) last[i]++;
        if (last[i] >= 0) last[i]--;
      }
    }
    last[0] = -1;
    for (int i = 0; i < n; i++) {
      for (int j = 2; j <= k; j++) {
        if (last[i] == -1)
          dp[i][j] = 0;
        else {
          dp[i][j] = psum[last[i]][j - 1];
        }
        psum[i][j] = dp[i][j];
        if (i) psum[i][j] += psum[i - 1][j];
        dp[i][j] %= mod;
        psum[i][j] %= mod;
      }
      ans += dp[i][k];
      ans %= mod;
    }
  }
  cout << ans << '\n';
  return 0;
}
