#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    string a;
    cin >> a;
    string b;
    cin >> b;
    string c = a;
    int flag = 0;
    int count = 0;
    vector<int> ans;
    int s = 1;
    int e = n;
    for (int i = n - 1; i >= 0; --i) {
      char x;
      if (flag == 0) {
        x = a[s - 1];
        ++s;
      } else {
        if (a[e - 1] == '0')
          x = '1';
        else
          x = '0';
        --e;
      }
      if (x != b[i]) {
        ++count;
        ans.push_back(i + 1);
      } else {
        count += 2;
        ans.push_back(1);
        ans.push_back(i + 1);
      }
      flag = 1 - flag;
    }
    cout << count << " ";
    for (auto it : ans) cout << it << " ";
    cout << endl;
  }
  return 0;
}
