#include <bits/stdc++.h>
using namespace std;
template <class T>
ostream& operator<<(ostream& cout, vector<T> V) {
  cout << "[ ";
  for (auto v : V) cout << v << ' ';
  return cout << ']';
}
template <class L, class R>
ostream& operator<<(ostream& cout, pair<L, R> P) {
  return cout << '(' << P.first << ',' << P.second << ')';
}
void invert(string& a, long long int ind) {
  for (long long int i = 0; i < (ind + 1); i++) {
    if (a[i] == '1')
      a[i] = '0';
    else
      a[i] = '1';
  }
  for (long long int i = 0, j = ind; i < j; i++, j--) swap(a[i], a[j]);
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    long long int n;
    cin >> n;
    string a, b;
    cin >> a >> b;
    string bac = a;
    vector<long long int> ans;
    long long int inv = 0, rev = 0;
    long long int l = 0, r = n - 1;
    for (long long int i = n - 1; i >= 0; i--) {
      if (rev) {
        if (inv) {
          if (a[l] == b[i]) {
            if (a[l] == a[r]) {
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            } else {
              if (a[r] == '0')
                a[r] = '1';
              else
                a[r] = '0';
              ans.push_back(0);
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            }
          }
        } else {
          if (a[l] != b[i]) {
            if (a[l] == a[r]) {
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            } else {
              if (a[r] == '0')
                a[r] = '1';
              else
                a[r] = '0';
              ans.push_back(0);
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            }
          }
        }
        if (rev)
          l++;
        else
          r--;
      } else {
        if (inv) {
          if (a[r] == b[i]) {
            if (a[l] == a[r]) {
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            } else {
              if (a[l] == '0')
                a[l] = '1';
              else
                a[l] = '0';
              ans.push_back(0);
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            }
          }
        } else {
          if (a[r] != b[i]) {
            if (a[l] == a[r]) {
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            } else {
              if (a[l] == '0')
                a[l] = '1';
              else
                a[l] = '0';
              ans.push_back(0);
              ans.push_back(i);
              inv = 1 - inv;
              rev = 1 - rev;
            }
          }
        }
        if (!rev)
          r--;
        else
          l++;
      }
    }
    cout << ans.size() << ' ';
    for (long long int i : ans) cout << i + 1 << ' ';
    cout << '\n';
  }
  cerr << "Time : " << 1000 * (long double)clock() / (long double)CLOCKS_PER_SEC
       << "ms\n";
  ;
}
