description: This is an easier version of the problem with smaller constraints.
  
  Korney Korneevich dag up an array a of length n. Korney Korneevich has recently read about the operation [bitwise XOR](https://en.wikipedia.org/wiki/Bitwise_operation#XOR), so he wished to experiment with it. For this purpose, he decided to find all integers x ≥ 0 such that there exists an increasing subsequence of the array a, in which the bitwise XOR of numbers is equal to x.
  
  It didn't take a long time for Korney Korneevich to find all such x, and he wants to check his result. That's why he asked you to solve this problem!
  
  A sequence s is a subsequence of a sequence b if s can be obtained from b by deletion of several (possibly, zero or all) elements.
  
  A sequence s_1, s_2, … , s_m is called increasing if s_1 < s_2 < … < s_m.
  
  Input
  
  The first line contains a single integer n (1 ≤ n ≤ 10^5).
  
  The second line contains n integers a_1, a_2, …, a_n (0 ≤ a_i ≤ 500) — the elements of the array a.
  
  Output
  
  In the first line print a single integer k — the number of found x values.
  
  In the second line print k integers in increasing order x_1, x_2, … x_k (0 ≤ x_1 < … < x_k) — found x values.
  
  Examples
  
  Input
  
  
  4
  4 2 2 4
  
  
  Output
  
  
  4
  0 2 4 6 
  
  
  Input
  
  
  8
  1 0 1 7 12 5 3 2
  
  
  Output
  
  
  12
  0 1 2 3 4 5 6 7 10 11 12 13 
  
  Note
  
  In the first test case:
  
    * To get value x = 0 it is possible to choose and empty subsequence 
    * To get value x = 2 it is possible to choose a subsequence [2] 
    * To get value x = 4 it is possible to choose a subsequence [4] 
    * To get value x = 6 it is possible to choose a subsequence [2, 4] 
solution: #include <bits/stdc++.h>
  #pragma GCC optimize("Ofast")
  #pragma GCC optimization("unroll-loops, no-stack-protector")
  #pragma GCC target("avx,avx2,fma")
  using namespace std;
  using pii = pair<int, int>;
  using pll = pair<long long, long long>;
  using vb = vector<bool>;
  using vi = vector<int>;
  using vl = vector<long long>;
  using vpii = vector<pair<int, int>>;
  using vvb = vector<vector<bool>>;
  using vvi = vector<vector<int>>;
  using vvl = vector<vector<long long>>;
  using vvpii = vector<vector<pair<int, int>>>;
  using mii = map<int, int>;
  using umii = unordered_map<int, int>;
  using seti = set<int>;
  using useti = unordered_set<int>;
  int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    vb res(8200);
    vvi store(8200, vi(1, 0));
    vvb seen(8200, vb(8200));
    res[0] = 1;
    for (int i = 0; i < (8200); i++) seen[i][0] = true;
    for (int i = 0; i < (n); i++) {
      int x;
      cin >> x;
      for (auto d : store[x]) {
        int y = d ^ x;
        res[y] = true;
        for (int j = x + 1; j < 8200; j++)
          if (!seen[j][y]) {
            seen[j][y] = true;
            store[j].push_back(y);
          } else
            break;
      }
      store[x].clear();
    }
    int ans = 0;
    for (int i = 0; i < (8200); i++) ans += res[i];
    cout << ans << "\n";
    for (int i = 0; i < (8200); i++)
      if (res[i]) cout << i << " ";
    cout << "\n";
  }
  