#include <bits/stdc++.h>
using namespace std;
const int N = 1000, mod = 998244353;
int n, m, a[N + 1];
int res;
int read() {
  int ret = 0;
  char c = getchar();
  while (!isdigit(c)) {
    c = getchar();
  }
  while (isdigit(c)) {
    ret = ret * 10 + c - '0';
    c = getchar();
  }
  return ret;
}
int calc(int lim) {
  static int f[N + 1][N + 1], s[N + 1][N + 1];
  int ret = 0;
  f[0][0] = 1;
  for (int i = 0; i <= n; ++i) {
    s[i][0] = 1;
  }
  for (int i = 1, j = 0; i <= n; ++i) {
    while (a[j + 1] <= a[i] - lim) {
      ++j;
    }
    for (int k = 1; k <= m; ++k) {
      f[i][k] = s[j][k - 1];
      s[i][k] = (s[i - 1][k] + f[i][k]) % mod;
    }
    ret = (ret + f[i][m]) % mod;
  }
  return ret;
}
int main() {
  n = read(), m = read();
  for (int i = 1; i <= n; ++i) {
    a[i] = read();
  }
  sort(a + 1, a + n + 1);
  for (int i = (a[n] - a[1]) / (m - 1), lv = 0; i; --i) {
    int nv = calc(i);
    res = (res + 1ll * i * (nv - lv)) % mod;
    lv = nv;
  }
  printf("%d\n", (res + mod) % mod);
  return 0;
}
