#include <bits/stdc++.h>
using namespace std;
void solve() {
  string s, t;
  cin >> s >> t;
  int n = s.size();
  int a[2][2] = {};
  int b[2][2] = {};
  for (int i = 0; i < n; i += 2) {
    a[s[i] - '0'][s[i + 1] - '0']++;
    b[t[i] - '0'][t[i + 1] - '0']++;
  }
  if (a[0][0] != b[0][0] || a[1][1] != b[1][1]) {
    cout << "-1\n\n";
    return;
  }
  vector<int> res;
  int x = a[0][1] - a[1][0];
  int y = b[1][0] - b[0][1];
  int p = -1;
  if (x != y) {
    int d = 0;
    for (int i = 0; i < n; i += 2) {
      if (s.substr(i, 2) == "01") d -= 2;
      if (s.substr(i, 2) == "10") d += 2;
      if (x + d == y) {
        res.push_back(i + 2);
        reverse(s.begin(), s.begin() + i + 2);
        goto handy;
      }
    }
    d = 0;
    for (int i = 0; i < n; i += 2) {
      if (t.substr(i, 2) == "01") d += 2;
      if (t.substr(i, 2) == "10") d -= 2;
      if (x == y + d) {
        p = i + 2;
        reverse(t.begin(), t.begin() + p);
        goto handy;
      }
    }
  }
handy:
  for (int i = 0; i < n; i += 2) {
    int j = n - i - 2;
    auto target = t.substr(j, 2);
    swap(target[0], target[1]);
    for (int k = i; k < n; k += 2) {
      if (s.substr(k, 2) == target) {
        if (k) {
          res.push_back(k);
          reverse(s.begin(), s.begin() + k);
        }
        res.push_back(k + 2);
        reverse(s.begin(), s.begin() + k + 2);
        break;
      }
    }
  }
  assert(s == t);
  if (p != -1) {
    res.push_back(p);
  }
  cout << res.size() << "\n";
  for (auto& x : res) {
    cout << x << ' ';
  }
  cout << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  cin >> t;
  while (t--) solve();
  cout << endl;
}
