#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int s = 0, w = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') w = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
  return s * w;
}
int a[1003];
long long x[1003][1003];
int main() {
  int n = read(), m = read();
  for (int i = 1; i <= n; i++) a[i] = read();
  a[0] = -1919810;
  sort(a + 1, a + n + 1);
  int Max = a[n];
  long long ans = 0;
  for (int t = 1; t * (m - 1) <= a[n]; t++) {
    int tmp = 0;
    for (int i = 0; i <= n; i++) x[i][0] = 1;
    for (int i = 1; i <= n; i++) {
      while (a[tmp] <= a[i] - t) tmp++;
      for (int j = 1; j <= m; j++)
        x[i][j] = (x[i - 1][j] + x[tmp - 1][j - 1]) % 998244353LL;
    }
    ans += x[n][m], ans %= 998244353LL;
  }
  cout << ans << endl;
  return 0;
}
