#include <bits/stdc++.h>
using namespace std;
const int INF = (int)INT_MAX;
const long long INF64 = (long long)1e18;
const long double eps = 1e-9;
const long double pi = 3.14159265358979323846;
double PHI = 1.6180339;
template <class T1>
void deb(T1 e) {
  cout << "-->" << e << "\n";
}
template <class T1, class T2>
void deb(T1 e1, T2 e2) {
  cout << "-->" << e1 << " " << e2 << "\n";
}
template <class T1, class T2, class T3>
void deb(T1 e1, T2 e2, T3 e3) {
  cout << "-->" << e1 << " " << e2 << " " << e3 << "\n";
}
template <class T1, class T2, class T3, class T4>
void deb(T1 e1, T2 e2, T3 e3, T4 e4) {
  cout << "-->" << e1 << " " << e2 << " " << e3 << " " << e4 << "\n";
}
template <class c>
struct rge {
  c b, e;
};
template <class c>
rge<c> range(c i, c j) {
  return rge<c>{i, j};
}
template <class c>
auto dud(c* x) -> decltype(cerr << *x, 0);
template <class c>
char dud(...);
struct debug {
  template <class c>
  debug& operator<<(const c&) {
    return *this;
  }
};
void read(vector<int>& v) {
  int N = (int)v.size();
  for (int i = 0; i < N; i++) {
    cin >> v[i];
  }
}
void Answer() {
  int n;
  cin >> n;
  string a, b;
  cin >> a >> b;
  if (a == b) {
    cout << "0"
         << "\n";
    return;
  };
  int r = n - 1;
  bool tog = false;
  vector<int> ans;
  int lll = 0, rrr = n - 1;
  while (r >= 0) {
    char A = (tog ? (a[lll] == '1' ? '0' : '1') : a[lll]);
    char B = (tog ? (a[rrr] == '1' ? '0' : '1') : a[rrr]);
    debug() << " ["
            << "lll"
               ": "
            << (lll)
            << "] "
               " ["
            << "rrr"
               ": "
            << (rrr)
            << "] "
               " ["
            << "r"
               ": "
            << (r)
            << "] "
               " ["
            << "A"
               ": "
            << (A)
            << "] "
               " ["
            << "B"
               ": "
            << (B)
            << "] "
               " ["
            << "b[r]"
               ": "
            << (b[r]) << "] ";
    if ((!r ? A : B) == b[r]) {
      --r;
      if (lll < rrr)
        --rrr;
      else
        ++rrr;
    } else if (A == b[r]) {
      ans.push_back(1);
      ans.push_back(r-- + 1);
      tog = !tog;
      swap(lll, rrr);
      if (lll < rrr)
        --rrr;
      else
        ++rrr;
    } else {
      ans.push_back(r-- + 1);
      tog = !tog;
      swap(lll, rrr);
      if (lll < rrr)
        --rrr;
      else
        ++rrr;
    }
  }
  cout << int((ans).size()) << ' ';
  for (auto x : ans) cout << x << ' ';
  cout << "\n";
  ;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int t = 1;
  cin >> t;
  while (t--) {
    Answer();
  }
  return 0;
}
