#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}
vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++) ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}
template <typename T>
bool MinPlace(T& a, const T& b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
bool MaxPlace(T& a, const T& b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename S, typename T>
ostream& operator<<(ostream& out, const pair<S, T>& p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}
template <typename T>
ostream& operator<<(ostream& out, const vector<T>& v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1) out << ", ";
  }
  out << "]";
  return out;
}
template <class TH>
void _dbg(const char* name, TH val) {
  clog << name << ": " << val << endl;
}
template <class TH, class... TA>
void _dbg(const char* names, TH curr_val, TA... vals) {
  while (*names != ',') clog << *names++;
  clog << ": " << curr_val << ", ";
  _dbg(names + 1, vals...);
}
void check(string A, string B, vector<int> moves) {
  for (int x : moves) {
    for (int i = 0; i <= x; i++) A[i] = (A[i] == '0') ? '1' : '0';
    for (int i = 0; i < x - i; i++) swap(A[i], A[x - i]);
  }
  assert(A == B);
}
void solve() {
  int N;
  cin >> N;
  string A;
  string B;
  cin >> A >> B;
  int cnt = 0;
  int sum = 0;
  auto get_val = [&](int id) {
    if (cnt % 2 == 0) return A[sum + id];
    return (A[sum - id] == '0') ? '1' : '0';
  };
  vector<int> moves;
  for (int i = N - 1; i >= 0; i--) {
    if (get_val(i) == B[i]) continue;
    if (B[i] != get_val(0))
      moves.push_back(i);
    else {
      moves.push_back(0);
      moves.push_back(i);
    }
    cnt++;
    if (cnt % 2)
      sum = sum + i;
    else
      sum = sum - i;
  }
  cout << moves.size() << " ";
  for (int x : moves) cout << x + 1 << " ";
  cout << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T;
  cin >> T;
  for (int t = 0; t < T; t++) solve();
}
