func_code_string: #include <bits/stdc++.h>   using namespace std;   using ll = long long;   using ld = long double;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(nullptr);     ll t;     cin >> t;     for (ll i = 0; i < t; i++) {       ll n;       cin >> n;       vector<ll> in(n);       vector<ll> count(n + 1);       for (ll i = 0; i < n; i++) {         cin >> in[i];         count[in[i]]++;       }       vector<ll> ops;       while (true) {         ll mex = 0;         while (count[mex] > 0) mex++;         if (mex < n) {           ops.push_back(mex);           count[in[mex]]--;           in[mex] = mex;           count[mex]++;         } else {           ll j = 0;           while (in[j] == j) j++;           if (j >= n) break;           ops.push_back(j);           count[in[j]]--;           in[j] = mex;           count[mex]++;         }       }       cout << (ll)(ops).size() << endl;       for (ll x : ops) {         cout << x + 1 <<    ;       }       cout << endl;     }   }   