#include <bits/stdc++.h>
using namespace std;
const int mod = 998244353, N = 1005, M = N * 100, inf = 0x3f3f3f3f;
inline int add(int a, int b) { return a + b >= mod ? a + b - mod : a + b; }
inline int sub(int a, int b) { return a >= b ? a - b : a - b + mod; }
inline int mul(int a, int b) { return 1ll * a * b % mod; }
int n, k, ans, a[N], f[N][N], sum[N][N], res[M];
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + n + 1);
  a[0] = -inf;
  int Max = a[n];
  for (int val = 1; val * (k - 1) <= Max; val++) {
    sum[0][0] = f[0][0] = 1;
    int pos = 0;
    for (int i = 1; i <= n; i++) {
      while (a[pos] <= a[i] - val) pos++;
      for (int j = 0; j <= k; j++) {
        if (j) f[i][j] = sum[pos - 1][j - 1];
        sum[i][j] = add(sum[i - 1][j], f[i][j]);
      }
      res[val] = add(f[i][k], res[val]);
    }
    ans = add(ans, res[val]);
  }
  cout << ans << endl;
  return 0;
}
