#include <bits/stdc++.h>   using namespace std;   int32_t main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int tc;     cin >> tc;     while (tc--) {       int n;       cin >> n;       string s, t;       cin >> s >> t;       vector<int> v, c;       for (int i = 1; i < n; i++) {         if (s[i] != s[i - 1]) v.push_back(i);       }       if (s[n - 1] != t[n - 1]) v.push_back(n);       for (int i = 1; i < n; i++) {         if (t[i] != t[i - 1]) c.push_back(i);       }       reverse(c.begin(), c.end());       cout << (int)v.size() + (int)c.size() <<    ;       for (int val : v) cout << val <<    ;       for (int val : c) cout << val <<    ;       cout <<   n ;     }     return 0;   }   