#include <bits/stdc++.h>
using namespace std;
int T, n, cnta[4], cntb[4], dy[2][2], ans[4040], k;
char a[4040], b[4040];
int main() {
  dy[0][0] = 0, dy[0][1] = 1, dy[1][0] = 2, dy[1][1] = 3;
  scanf("%d", &T);
  while (T--) {
    scanf("%s %s", a + 1, b + 1);
    n = strlen(a + 1);
    k = 0;
    for (int i = 1; i <= n; ++i) a[i] -= '0', b[i] -= '0';
    cnta[0] = cnta[1] = cnta[2] = cnta[3] = 0;
    for (int i = 2; i <= n; i += 2) ++cnta[dy[a[i - 1]][a[i]]];
    cntb[0] = cntb[1] = cntb[2] = cntb[3] = 0;
    for (int i = 2; i <= n; i += 2) ++cntb[dy[b[i - 1]][b[i]]];
    if (cnta[0] != cntb[0] || cnta[3] != cntb[3]) {
      printf("-1\n");
      continue;
    }
    if (abs(cnta[1] - cnta[2]) >= abs(cntb[1] - cntb[2])) {
      if (cnta[1] != cntb[2]) {
        int now = 0;
        for (int i = 2; i <= n; i += 2) {
          if (dy[a[i - 1]][a[i]] == 1) ++now;
          if (dy[a[i - 1]][a[i]] == 2) --now;
          if (cnta[1] - cnta[2] - 2 * now == cntb[2] - cntb[1]) {
            reverse(a + 1, a + i + 1);
            ans[++k] = i;
            break;
          }
        }
      }
      for (int i = 2; i <= n; i += 2) {
        int p, c = dy[b[n - i + 2]][b[n - i + 1]];
        for (int j = i; j <= n; j += 2)
          if (dy[a[j - 1]][a[j]] == c) {
            p = j;
            break;
          }
        reverse(a + 1, a + 1 + p - 2), ans[++k] = p - 2;
        reverse(a + 1, a + 1 + p), ans[++k] = p;
      }
      int cnt = 0;
      for (int i = 1; i <= k; ++i)
        if (ans[i]) {
          if (cnt && ans[i] == ans[cnt])
            --cnt;
          else
            ans[++cnt] = ans[i];
        }
      printf("%d\n", cnt);
      for (int i = 1; i <= cnt; ++i) printf("%d ", ans[i]);
      printf("\n");
    } else {
      int now = 0;
      for (int i = 2; i <= n; i += 2) {
        if (dy[b[i - 1]][b[i]] == 1) --now;
        if (dy[b[i - 1]][b[i]] == 2) ++now;
        if (cnta[1] - cnta[2] == cntb[2] - cntb[1] - 2 * now) {
          reverse(b + 1, b + i + 1);
          ans[++k] = i;
          break;
        }
      }
      for (int i = 2; i <= n; i += 2) {
        int p, c = dy[a[n - i + 2]][a[n - i + 1]];
        for (int j = i; j <= n; j += 2)
          if (dy[b[j - 1]][b[j]] == c) {
            p = j;
            break;
          }
        reverse(b + 1, b + 1 + p - 2), ans[++k] = p - 2;
        reverse(b + 1, b + 1 + p), ans[++k] = p;
      }
      reverse(ans + 1, ans + 1 + k);
      int cnt = 0;
      for (int i = 1; i <= k; ++i)
        if (ans[i]) {
          if (cnt && ans[i] == ans[cnt])
            --cnt;
          else
            ans[++cnt] = ans[i];
        }
      printf("%d\n", cnt);
      for (int i = 1; i <= cnt; ++i) printf("%d ", ans[i]);
      printf("\n");
    }
  }
  return 0;
}
