#include <bits/stdc++.h>   using namespace std;   int64_t ans, n, k, m, r[100005];   char s[100005], t[100005];   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     int64_t tt;     cin >> tt;     while (tt--) {       cin >> n;       cin >> s;       cin >> t;       vector<int> ans;       m = n - 1;       int i = 0, j = n - 1;       while (i < j) {         r[m--] = i;         i++;         r[m--] = j;         j--;       }       if (i == j) r[m] = i;       m = 0;       for (int i = n - 1; i >= 0; i--) {         if ((s[r[i]] -  0  + m) % 2 == t[i] -  0 ) ans.push_back(1);         ans.push_back(i + 1);         m++;       }       cout << (int)ans.size() <<    ;       for (auto i : ans) cout << i <<    ;       cout <<   n ;     }     return 0;   }   