#include <bits/stdc++.h>
using namespace std;
const int P = 998244353;
int n, k;
int dp[2222][1111], a[2222];
template <typename T>
inline void chkmax(T &x, T y) {
  x = max(x, y);
}
template <typename T>
inline void chkmin(T &x, T y) {
  x = min(x, y);
}
template <typename T>
inline void read(T &x) {
  T f = 1;
  x = 0;
  char c = getchar();
  for (; !isdigit(c); c = getchar())
    if (c == '-') f = -f;
  for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
  x *= f;
}
int main() {
  read(n);
  read(k);
  for (int i = 1; i <= n; ++i) read(a[i]);
  sort(a + 1, a + n + 1);
  int ans = 0;
  for (int i = (int)1e5 / (k - 1); i >= 1; --i) {
    int pt = 1;
    for (int j = 1; j <= n; ++j) {
      while (pt < j && a[j] - a[pt] >= i) ++pt;
      dp[j][2] = (dp[j - 1][2] + pt - 1) % P;
      for (int K = 3; K <= k; ++K)
        dp[j][K] = (1ll * dp[j - 1][K] + dp[pt - 1][K - 1]) % P;
    }
    ans = (ans + dp[n][k]) % P;
  }
  printf("%d\n", ans);
  return 0;
}
