#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int q = 0, w = 1;
  char c = getchar();
  while (!isdigit(c)) {
    if (c == '-') w = -1;
    c = getchar();
  }
  while (isdigit(c)) q = q * 10 + c - '0', c = getchar();
  return w * q;
}
const int N = 1010;
const int mod = 998244353;
int n, k, ans, a[N], dp[N][N], sum[N][N];
int main() {
  n = read();
  k = read();
  for (int i = 1; i <= n; ++i) a[i] = read();
  sort(a + 1, a + 1 + n);
  for (int gap = 1; gap <= (a[n] - a[1]) / (k - 1); ++gap) {
    for (int i = 0; i <= n; ++i)
      for (int j = 0; j <= k; ++j) dp[i][j] = sum[i][j] = 0;
    for (int i = 1; i <= n; ++i) dp[i][1] = 1, sum[i][1] = i;
    for (int j = 2; j <= k; ++j) {
      int cur = 0;
      for (int i = 1; i <= n; ++i) {
        while (cur < i && a[i] - a[cur + 1] >= gap) cur++;
        dp[i][j] = sum[cur][j - 1];
        sum[i][j] = (sum[i - 1][j] + dp[i][j]) % mod;
      }
    }
    ans = (ans + sum[n][k]) % mod;
  }
  cout << ans << endl;
  return 0;
}
