#include <bits/stdc++.h>
long long read() {
  long long x = 0, f = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = x * 10 + c - '0';
    c = getchar();
  }
  return x * f;
}
using namespace std;
const long long maxn = 1e3 + 7;
const double eps = 1e-10;
const long long mod = 1e9 + 7;
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    string a, b;
    cin >> a >> b;
    long long now = n - 1;
    long long sum = 0;
    vector<long long> ans;
    long long L = 0, R = n - 1;
    while (now >= 0) {
      if (now == 0) {
        if (sum & 1) {
          if (a[L] == b[0]) ans.push_back(1);
        } else if (a[L] != b[0])
          ans.push_back(1);
      } else {
        long long l, r;
        if (sum & 1) {
          l = !(a[R] - '0');
          r = !(a[L] - '0');
          if (r == b[now] - '0') {
            L++;
          } else {
            R--;
            if (l == b[now] - '0') {
              ans.push_back(1);
              ans.push_back(now + 1);
              sum++;
            } else {
              ans.push_back(now + 1);
              sum++;
            }
          }
        } else {
          l = a[L] - '0';
          r = a[R] - '0';
          if (r == b[now] - '0') {
            R--;
          } else {
            L++;
            if (l == b[now] - '0') {
              ans.push_back(1);
              ans.push_back(now + 1);
              sum++;
            } else {
              ans.push_back(now + 1);
              sum++;
            }
          }
        }
      }
      now--;
    }
    cout << (long long)ans.size();
    for (long long i = 0; i < ans.size(); i++) cout << ' ' << ans[i];
    cout << "\n";
  }
}
