#include <bits/stdc++.h>
using namespace std;
namespace fastIO1 {
inline char read() {
  static const int IN_LEN = 1000000;
  static char buf[IN_LEN], *s, *t;
  return (s == t               ? t = (s = buf) + fread(buf, 1, IN_LEN, stdin),
          (s == t ? -1 : *s++) : *s++);
}
template <class T>
inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = read(); !isdigit(c); c = read()) {
    if (c == '-') iosig = true;
    if (c == -1) return;
  }
  for (x = 0; isdigit(c); c = read()) x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig) x = -x;
}
inline char readc(char &c) {
  for (c = read(); !isalpha(c) && !isdigit(c); c = read())
    if (c == -1) return 0;
}
const int OUT_LEN = 10000000;
char obuf[OUT_LEN], *ooh = obuf;
inline void print(char c) {
  if (ooh == obuf + OUT_LEN) fwrite(obuf, 1, OUT_LEN, stdout), ooh = obuf;
  *ooh++ = c;
}
template <class T>
inline void print(T x) {
  static int buf[30], cnt;
  if (x == 0)
    print('0');
  else {
    if (x < 0) print('-'), x = -x;
    for (cnt = 0; x; x /= 10) buf[++cnt] = x % 10 + 48;
    while (cnt) print((char)buf[cnt--]);
  }
}
inline void flush() { fwrite(obuf, 1, ooh - obuf, stdout); }
}  // namespace fastIO1
namespace fastIO2 {
template <class T>
inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = getchar(); !isdigit(c); c = getchar()) {
    if (c == '-') iosig = true;
    if (c == -1) return;
  }
  for (x = 0; isdigit(c); c = getchar()) x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig) x = -x;
}
}  // namespace fastIO2
using namespace fastIO1;
int n, m, mx, ans, a[(1010)], f[(1010)][(1010)];
int main() {
  read(n), read(m);
  for (int i = 1; i <= n; i++) read(a[i]);
  sort(a + 1, a + n + 1), a[0] = -(0x7f7f7f7f);
  for (int k = 1; k <= a[n] / (m - 1); k++) {
    f[0][0] = 1;
    for (int i = 1, p = 1; i <= n; i++) {
      for (; a[i] - a[p] >= k; p++)
        ;
      for (int j = 0; j <= m; j++) f[i][j] = 0;
      for (int j = 1; j <= m; j++) f[i][j] = f[p - 1][j - 1];
      for (int j = 0; j <= m; j++) (f[i][j] += f[i - 1][j]) %= (998244353);
    }
    (ans += f[n][m]) %= (998244353);
  }
  cout << ans;
}
