#define ll long long #define pub push_back #define pob pop_back #define puf push_front #define pof pop_front #define mp make_pair #define fo(i , n) for(ll i = 0 ; i < n ; i++) //#include<bits/stdc++.h> #include<iomanip> #include<cmath> #include<cstdio> #include<utility> #include<iostream> #include<vector> #include<string> #include<algorithm> #include<map> #include<queue> #include<set> #include<stack> ll pi = acos(-1) ; ll z = 1000000007 ; ll inf = 100000000000000000 ; ll p1 = 37 ; ll p2 = 53 ; ll mod1 = 202976689 ; ll mod2 = 203034253 ; const int NN = 3e2 ; ll fact[NN]; ll gdp(ll a , ll b){return (a - (a%b)) ;} ll ld(ll a , ll b){if(a < 0) return -1*gdp(abs(a) , b) ; if(a%b == 0) return a ; return (a + (b - a%b)) ;} // least number >=a divisible by b ll gd(ll a , ll b){if(a < 0) return(-1 * ld(abs(a) , b)) ; return (a - (a%b)) ;} // greatest number <= a divisible by b ll gcd(ll a , ll b){ if(b > a) return gcd(b , a) ; if(b == 0) return a ; return gcd(b , a%b) ;} ll e_gcd(ll a , ll b , ll &x , ll &y){ if(b > a) return e_gcd(b , a , y , x) ; if(b == 0){x = 1 ; y = 0 ; return a ;} ll x1 , y1 ; e_gcd(b , a%b , x1 , y1) ; x = y1 ; y = (x1 - ((a/b) * y1)) ; return e_gcd(b , a%b , x1 , y1) ;} ll power(ll a ,ll b , ll p){if(b == 0) return 1 ; ll c = power(a , b/2 , p) ; if(b%2 == 0) return ((c*c)%p) ; else return ((((c*c)%p)*a)%p) ;} ll inverse(ll a ,ll n){return power(a , n-2 , n) ;} ll max(ll a , ll b){if(a > b) return a ; return b ;} ll min(ll a , ll b){if(a < b) return a ; return b ;} ll left(ll i){return ((2*i)+1) ;} ll right(ll i){return ((2*i) + 2) ;} ll ncr(ll n , ll r){if(n < r) return 0 ; return ((((fact[n] * inverse(fact[r] , z)) % z) * inverse(fact[n-r] , z)) % z);} void swap(ll&a , ll&b){ll c = a ; a = b ; b = c ; return ;} //ios_base::sync_with_stdio(0); //cin.tie(0); cout.tie(0); using namespace std ; #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using namespace __gnu_pbds; #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> #define pll pair<ll, ll> // ordered_set s ; s.order_of_key(val) no. of elements strictly less than val // s.find_by_order(i) itertor to ith element (0 indexed) //__builtin_popcount(n) -> returns number of set bits in n ll get_ans(ll n, ll arr[] , ll bits, ll val) { ll ans = inf ; map<ll ,ll> m ; ll curr_arr[n] ; for(int i = 0 ; i < n ; i++) { curr_arr[i] = ((arr[i]) >> (int)bits) ; } ll pre_xor = 0 ; m[0] = -1 ; for(int i = 0 ; i < n ; i++) { pre_xor ^= curr_arr[i] ; ll req_xor = (val ^ pre_xor) ; if(m.find(req_xor) == m.end()) { m[pre_xor] = i ; continue ; } ll curr_ans = (i - m[req_xor]) ; ans = min(ans , curr_ans) ; m[pre_xor] = i ; } return ans ; } void solve() { ll n, k ; cin >> n >> k ; ll arr[n] ; for(int i = 0 ; i < n ; i++) cin >> arr[i] ; ll curr_val = 0 ; ll ans = inf ; for(int i = 31 ; i >= 0 ; i--) { ll bit = ((1LL << i) & k) ; // cout << "bit = " << bit << endl ; curr_val *= 2 ; if(bit != 0) { curr_val++ ; continue ; } ans = min(ans , get_ans(n , arr , i , curr_val+1)) ; // cout << "i = " << i << " ans = " << ans << '\n' << endl ; } ans = min(ans , get_ans(n , arr , 0 , k)) ; if(ans == inf) ans = -1 ; cout << ans << endl ; } int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); #ifndef ONLINE_JUDGE freopen("inputf.txt" , "r" , stdin) ; freopen("outputf.txt" , "w" , stdout) ; freopen("errorf.txt" , "w" , stderr) ; #endif ll t = 1; cin >> t ; while(t--) { solve() ; } // cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n"; return 0; }