1. #include <bits/stdc++.h>
  2. #define ll long long int
  3. #define ld long double
  4. using namespace std;
  5.  
  6. ll n;
  7. vector<ll> v;
  8.  
  9. int solve(int bit, ll k)
  10. {
  11.   int ans = n + 1;
  12.   unordered_map<ll, int> m;
  13.   ll curr_xor = 0;
  14.   vector<ll> prefix_xor(n + 1);
  15.   for (int i = 0; i < n; i++)
  16.   {
  17.     ll curr = ((v[i] >> bit) << bit);
  18.     prefix_xor[i + 1] = curr;
  19.   }
  20.   for (int i = 1; i <= n; i++)
  21.   {
  22.     curr_xor ^= prefix_xor[i];
  23.     if (curr_xor == k)
  24.       ans = min(ans, i);
  25.     if (m[curr_xor ^ k])
  26.       ans = min(ans, i - m[curr_xor ^ k]);
  27.     m[curr_xor] = i;
  28.   }
  29.   return ans;
  30. }
  31.  
  32. void mainSolve()
  33. {
  34.   ll k;
  35.   cin >> n >> k;
  36.   v.clear();
  37.   v.resize(n);
  38.   for (int i = 0; i < n; i++)
  39.     cin >> v[i];
  40.   int ans = solve(0, k);
  41.   for (int bit = 30; bit >= 0; bit--)
  42.   {
  43.     if ((k >> bit) & 1)
  44.       continue;
  45.     ll curr_k = (((k >> bit) | 1) << bit);
  46.     ans = min(ans, solve(bit, curr_k));
  47.   }
  48.   if (ans == (n + 1))
  49.     ans = -1;
  50.   cout << ans << endl;
  51. }
  52.  
  53. int main()
  54. {
  55. #ifndef ONLINE_JUDGE
  56.   freopen("input.txt", "r", stdin);
  57.   freopen("output.txt", "w", stdout);
  58. #endif
  59.   int t;
  60.   cin >> t;
  61.   while (t--)
  62.   {
  63.     mainSolve();
  64.   }
  65.   return 0;
  66. }