I bought some credits. Here is the result (Python to C++):

  std::map<int, int> foobar(std::vector<int> x, std::vector<int> y) {
    std::map<int, int> map;

    for (int i = 0; i < x.size(); i++) {
      if (std::find(y.begin(), y.end(), x[i]) != y.end()) {
        map[x[i]] = x[i + 1];
      }
    }
    
    return map;
  }