#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
using namespace std;
long long int mod = 1000000007;
long long int maxn = 200001;
long long int binpow(long long int a, long long int b, long long int mod) {
  long long int res = 1;
  while (b > 0) {
    if (b % 2) {
      res = (res * a) % mod;
      b--;
    }
    a = (a * a) % mod;
    b /= 2;
  }
  return res % mod;
}
long long int binpow(long long int a, long long int b) {
  long long int res = 1;
  while (b > 0) {
    if (b % 2) {
      res = (res * a);
      b--;
    }
    a = (a * a);
    b /= 2;
  }
  return res;
}
bool isPrime(long long int n) {
  if (n == 1) return false;
  for (long long int i = 2; i * i <= n; i++) {
    if (n % i == 0) return false;
  }
  return true;
}
long long int mulmod(long long int a, long long int b) {
  return ((a % mod) * (b % mod)) % mod;
}
long long int addmod(long long int a, long long int b) {
  return (((a % mod) + (b % mod)) + mod) % mod;
}
void solve();
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int t = 2;
  cin >> t;
  for (long long int tt = 1; tt <= t; tt++) {
    solve();
  }
}
void solve() {
  long long int n;
  cin >> n;
  string s1, s2;
  cin >> s1 >> s2;
  vector<long long int> oper;
  bool zero;
  if (s1[0] == '0')
    zero = true;
  else
    zero = false;
  for (long long int i = 0; i < n - 1; i++) {
    if (s1[i] != s1[i + 1]) {
      oper.push_back(i + 1);
      zero = !zero;
    }
  }
  if (!zero) oper.push_back(n);
  s1 = string(n, '0');
  zero = true;
  for (long long int i = n - 1; i >= 0; i--) {
    if (s2[i] == '1' and zero == true) {
      oper.push_back(i + 1);
      zero = false;
    }
    if (s2[i] == '0' and zero == false) {
      oper.push_back(i + 1);
      zero = true;
    }
  }
  cout << oper.size() << " ";
  for (long long int i = 0; i < oper.size(); i++) cout << oper[i] << " ";
  cout << "\n";
}
