#include <bits/stdc++.h>
using namespace std;
long long inp, Inp;
long long i1, i2, i3, i4, i5, i6, i7, i8;
long long MOD = 998244353, MOD1 = (long long)1e9 + 7, MOD2 = (long long)1e9 + 9;
long long MOD3 = (long long)1e9 + 21;
double eps = 1e-9;
long long TMP =
    (chrono::high_resolution_clock::now().time_since_epoch().count() % MOD +
     MOD) %
    MOD;
auto STTMP = chrono::steady_clock::now();
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  std::cout.precision(20);
  srand((unsigned int)TMP);
  long long T;
  cin >> T;
  for (int t = (0); t < (T); t++) {
    long long N;
    cin >> N;
    string A;
    cin >> A;
    string B;
    cin >> B;
    long long pos = N - 1;
    long long abeg = 0, aend = N - 1;
    bool flipped = false;
    vector<long long> sol;
    while (pos >= 1) {
      if (A.at(abeg) == B.at(pos)) {
        sol.push_back(1);
      }
      sol.push_back(pos + 1);
      pos--;
      if (A.at(aend) != B.at(pos)) {
        sol.push_back(1);
      }
      sol.push_back(pos + 1);
      abeg++;
      aend--;
      pos--;
    }
    if (pos == 0) {
      if (A.at(abeg) != B.at(pos)) {
        sol.push_back(1);
      }
    }
    cout << sol.size() << " ";
    for (auto it : sol) {
      cout << it << " ";
    }
    cout << "\n";
  }
  return 0;
}
