下面程序的运行结果为（ ）。

bool check(int n, int a[], int k, int dist) {
    int cnt = 1;
    int last = a[0];
    for (int i = 1; i < n; i++) {
        if (a[i] - last >= dist) {
            cnt++;
            last = a[i];
        }
    }
    return cnt >= k;
}

int solve(int n, int a[], int k) {
    std::sort(a, a + n);
    int l = 0;
    int r = a[n - 1] - a[0];
    while (l < r) {
        int mid = (l + r + 1) / 2;
        if (check(n, a, k, mid))
            l = mid;
        else
            r = mid - 1;
    }
    return l;
}

int main() {
    int a[] = {1, 2, 8, 4, 9};
    int n = 5;
    int k = 3;
    std::cout << solve(n, a, k) << std::endl;
    return 0;
}