#include <bits/stdc++.h>
using namespace std;
const int c = 2002;
int w, n, kezd[c], veg[c], db[4];
string a, b;
vector<int> ans;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> w;
  while (w--) {
    cin >> a >> b;
    n = a.size();
    ans.clear();
    for (int i = 0; i < 4; i++) {
      db[i] = 0;
    }
    for (int i = 0; i < n; i++) {
      if (i % 2) {
        int x = 2 * (a[i - 1] == '1') + (a[i] == '1');
        db[x]++, kezd[i / 2] = x;
        int y = 2 * (b[i] == '1') + (b[i - 1] == '1');
        db[y]--, veg[i / 2] = y;
      }
    }
    n /= 2;
    if (db[0] || db[3]) {
      cout << -1 << "\n";
      continue;
    }
    int spec = 0;
    if (db[1]) {
      int dif = 0, dif2 = 0;
      for (int i = 0; i < n; i++) {
        if (kezd[i] == 1) {
          dif++;
        }
        if (kezd[i] == 2) {
          dif--;
        }
        if (veg[i] == 1) {
          dif2--;
        }
        if (veg[i] == 2) {
          dif2++;
        }
        if (dif == db[1]) {
          ans.push_back(i);
          for (int j = 0; j <= i; j++) {
            if (kezd[j] % 3) {
              kezd[j] = 3 - kezd[j];
            }
          }
          reverse(kezd, kezd + i + 1);
          break;
        }
        if (dif2 == db[1]) {
          spec = 2 * (i + 1);
          for (int j = 0; j <= i; j++) {
            if (veg[j] % 3) {
              veg[j] = 3 - veg[j];
            }
          }
          reverse(veg, veg + i + 1);
          break;
        }
      }
    }
    for (int i = 0; i < n; i++) {
    }
    for (int i = 0; i < n; i++) {
    }
    for (int i = 0; i < n; i++) {
      for (int j = i; j < n; j++) {
        if (kezd[j] == veg[n - i - 1]) {
          if (j) {
            ans.push_back(j - 1);
          }
          ans.push_back(j);
          for (int k = j; k > 0; k--) {
            swap(kezd[k], kezd[k - 1]);
          }
          break;
        }
      }
    }
    if (spec) {
      ans.push_back(spec / 2 - 1);
    }
    string aa = a;
    for (int x : ans) {
      int s = 2 * (x + 1);
      reverse(a.begin(), a.begin() + s);
    }
    if (a != b) {
      return 0;
    }
    cout << ans.size() << "\n";
    for (int x : ans) {
      int s = 2 * (x + 1);
      reverse(a.begin(), a.begin() + s);
      cout << 2 * (x + 1) << " ";
    }
    cout << "\n";
  }
  return 0;
}
