/* Problem URL: https://codeforces.com/problemset/problem/1904/C */

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template <class T, class comp = less<>>
using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (int i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

const int oo = INT32_MAX >> 1;
const ll OO = INT64_MAX >> 1;


void pre()
{

}

#define TEST 1

void solve()
{
    int n;
    ll k;
    cin >> n >> k;

    vl a(n);
    cin >> a;
    if (k >= 3) {
        cout << "0\n";
        return;
    }

    sort(all(a), greater<>());

    ll ans = *min_element(all(a));

    vl ot;

    rep(i, n - 1) {
        nrep(j, i + 1, n) {
            rmin(ans, max(a[i] - a[j] * k, a[i] % a[j]));

            if (k > 1) {
                ll cur = a[i] - a[j];
                int ind = lower_bound(all(a), cur, greater<>()) - a.begin();
                if (ind < n) {
                    rmin(ans, abs(a[ind] - cur));
                }

                if (ind < n - 1) {
                    rmin(ans, abs(a[ind + 1] - cur));
                }

                if (ind < n - 2) {
                    rmin(ans, abs(a[ind + 2] - cur));
                }

                if (ind > 0) {
                    rmin(ans, abs(a[ind - 1] - cur));
                }

                if (ind > 1) {
                    rmin(ans, abs(a[ind - 2] - cur));
                }

                rmin(ans, abs(cur - a[j]));
                rmin(ans, abs(cur - a[i]));
            }
        }
    }

    cout << ans << '\n';
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    pre();

    int t;
    (TEST && cin >> t) || (t = 1);
    while (t--) {
        solve();
    }
}