#include <bits/stdc++.h>
using namespace std;
vector<int> ans;
char a[4005], b[4005];
int main() {
  int cases;
  scanf("%d", &cases);
  for (; cases; cases--) {
    vector<int>().swap(ans);
    scanf("%s%s", a + 1, b + 1);
    int n = strlen(a + 1), s = 0;
    for (int i = 1; i <= n; i += 2) {
      if (a[i] == '1' && a[i + 1] == '1') s++;
      if (b[i] == '1' && b[i + 1] == '1') s--;
    }
    if (s) {
      puts("-1");
      continue;
    }
    for (int i = 1; i <= n; i += 2) {
      if (a[i] == '0' && a[i + 1] == '0') s++;
      if (b[i] == '0' && b[i + 1] == '0') s--;
    }
    if (s) {
      puts("-1");
      continue;
    }
    int s1 = 0, s2 = 0;
    for (int i = 1; i <= n; i += 2) {
      if (a[i] == '0' && a[i + 1] == '1') s1++;
      if (a[i] == '1' && a[i + 1] == '0') s1--;
      if (b[i] == '0' && b[i + 1] == '1') s2++;
      if (b[i] == '1' && b[i + 1] == '0') s2--;
    }
    bool v = 0;
    if (abs(s1) < abs(s2)) {
      for (int i = 1; i <= n; i++) swap(a[i], b[i]);
      v = 1;
      swap(s1, s2);
    }
    if (s1 != -s2) {
      int s = 0;
      for (int i = 1; i <= n; i += 2) {
        if (a[i] == '0' && a[i + 1] == '1') s++;
        if (a[i] == '1' && a[i + 1] == '0') s--;
        if (s1 - 2 * s == -s2) {
          ans.push_back(i + 1);
          reverse(a + 1, a + i + 2);
          break;
        }
      }
    }
    for (int i = 1; i <= n; i += 2) {
      if (b[n - i] == b[n - i + 1]) {
        for (int j = i; j <= n; j += 2)
          if (a[j] == b[n - i] && a[j + 1] == b[n - i + 1]) {
            if (j > 1) {
              ans.push_back(j - 1);
              reverse(a + 1, a + j);
            }
            ans.push_back(j + 1);
            reverse(a + 1, a + j + 2);
            break;
          }
      } else {
        for (int j = i; j <= n; j += 2)
          if (a[j + 1] == b[n - i] && a[j] == b[n - i + 1]) {
            if (j > 1) {
              ans.push_back(j - 1);
              reverse(a + 1, a + j);
            }
            ans.push_back(j + 1);
            reverse(a + 1, a + j + 2);
            break;
          }
      }
    }
    if (v) reverse(ans.begin(), ans.end());
    printf("%d\n", (int)ans.size());
    for (int i = 0; i < ans.size(); i++) printf("%d ", ans[i]);
    printf("\n");
  }
  return 0;
}
