#include <bits/stdc++.h>   using namespace std;   int main() {     ios::sync_with_stdio(false);     int t;     cin >> t;     while (t--) {       int n;       cin >> n;       string a, b;       a +=  M , b +=  M ;       string tmp1, tmp2;       cin >> tmp1 >> tmp2;       a += tmp1, b += tmp2;       for (int i = (1); i < n + 1; i++) a[i] -=  0 , b[i] -=  0 ;       vector<int> ans;       int pos = 1;       for (int i = (1); i < n + 1; i++) {         if (b[n - i + 1] == (a[pos] + i - 1) % 2) ans.push_back(1);         ans.push_back(n - i + 1);         if (pos <= n / 2)           pos = n - pos + 1;         else           pos = n - pos + 2;       }       cout << ans.size() <<    ;       for (auto p : ans) cout << p <<    ;       cout <<   n ;     }     return 0;   }   