What does the fox say? Solution:

#include <bits/stdc++.h>
using namespace std;

std::vector<std::string> stringSplit(const std::string &s, char delimiter){
   std::vector<std::string> tokens;
   std::string token;
   std::istringstream tokenStream(s);
   while (getline(tokenStream, token, delimiter)){
      tokens.push_back(token);
   }
   return tokens;
}

int main() {
    // #ifndef TESTING
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    // #endif

    string line;
    getline(cin, line);
    int n_cases = stoi(line);
    while(n_cases--){
        getline(cin, line);
        set<string> s;
        auto forest_sounds = stringSplit(line, ' ');
        for_each(forest_sounds.begin(), forest_sounds.end(), [&s = s](const string &sound){ s.insert(sound);});
        while(line != "what does the fox say?"){
            getline(cin, line);
            s.erase(stringSplit(line, ' ')[2]);
        }
        forest_sounds.erase(remove_if(forest_sounds.begin(), forest_sounds.end(), [&s = s, end = s.end()](const string &x){ return (s.find(x) == end);}), forest_sounds.end());
        for_each(forest_sounds.begin(), forest_sounds.end(), [](const string &s){ cout << s << " ";});
        cout << endl;
    }

    return 0;
}