#include <bits/stdc++.h>   using namespace std;   int main(void) {     int t;     cin >> t;     while (t--) {       int n;       cin >> n;       vector<int> ans1, ans2;       string a, b;       cin >> a >> b;       a = a +  0 ;       b = b +  0 ;       for (int i = 0; i < n; i++) {         if (a[i] != a[i + 1]) ans1.push_back(i);       }       for (int i = 0; i < n; i++) {         if (b[i] != b[i + 1]) ans2.push_back(i);       }       cout << ans1.size() + ans2.size() <<    ;       for (int i = 0; i < ans1.size(); i++) cout << ans1[i] + 1 <<    ;       for (int i = ans2.size() - 1; i >= 0; i--) cout << ans2[i] + 1 <<    ;       cout <<   n ;     }     return 0;   }   