#include <bits/stdc++.h>
using namespace std;
int a[4001], b[4001], sum[4], Sum[4], Q, n, N, i, j, k, l, Ls, tot;
int ans[4002];
char S[4001], T[4001];
void swap(int &x, int &y) {
  int z = x;
  x = y;
  y = z;
}
int turn(char a, char b) {
  if (a == b) {
    return (a == '0') ? 2 : 3;
  }
  if (a == '0') return 0;
  return 1;
}
void rev(int *a, int t) {
  int i;
  for (i = t / 2; i >= 1; i--) swap(a[i], a[t - i + 1]);
  for (i = 1; i <= t; i++)
    if (a[i] <= 1) a[i] ^= 1;
}
int main() {
  scanf("%d", &Q);
  for (; Q; --Q) {
    scanf("%s", S + 1), scanf("%s", T + 1);
    n = strlen(S + 1), tot = 0, N = n / 2;
    memset(sum, 0, sizeof(sum));
    memset(Sum, 0, sizeof(Sum));
    for (i = 1; i <= N; i++) a[i] = turn(S[i * 2 - 1], S[i * 2]), ++sum[a[i]];
    for (i = 1; i <= N; i++) b[i] = turn(T[i * 2 - 1], T[i * 2]), ++Sum[b[i]];
    if (sum[0] + sum[1] != sum[0] + sum[1] || sum[2] != Sum[2] ||
        sum[3] != Sum[3]) {
      printf("-1\n");
      continue;
    }
    Ls = -1, tot = 0;
    if (sum[0] != Sum[0]) {
      if (((sum[0] - sum[1]) > 0 ? (sum[0] - sum[1]) : -(sum[0] - sum[1])) >
          ((Sum[0] - Sum[1]) > 0 ? (Sum[0] - Sum[1]) : -(Sum[0] - Sum[1]))) {
        for (i = 1; i <= N; i++)
          if (a[i] <= 1) {
            --sum[a[i]], ++sum[a[i] ^ 1];
            if (sum[0] == Sum[0]) {
              rev(a, i);
              ans[++tot] = i;
              break;
            }
          }
      } else {
        for (i = 1; i <= N; i++)
          if (b[i] <= 1) {
            --Sum[b[i]], ++Sum[b[i] ^ 1];
            if (sum[0] == Sum[0]) {
              rev(b, i);
              Ls = i;
              break;
            }
          }
      }
    }
    for (i = 1; i <= N - 1; i++) {
      for (j = i; j <= N; j++)
        if (a[j] == b[i]) {
          if (j > 1) rev(a, j - 1), ans[++tot] = j - 1;
          rev(a, j), ans[++tot] = j;
          break;
        }
    }
    if (N > 1) rev(a, N - 1), ans[++tot] = N - 1;
    if (Ls > -1) ans[++tot] = Ls;
    printf("%d\n", tot);
    for (i = 1; i <= tot; i++) printf("%d ", ans[i] * 2);
    printf("\n");
  }
}
