#include <algorithm>
#include <iostream>
#include <vector>
#include <unordered_map>
 
using user = int;
using uint32 = unsigned long int;
 
int main()
{
    std::unordered_map<uint32, user> myMap = {{1,2},{3,5},{2,9},{4,7}};
    std::vector<uint32> to_find = {1,3};
    std::vector<user> results;
 
    if(to_find.size() == 0)  // if you have to_find vec size = 0
        std::for_each(myMap.cbegin(), myMap.cend(), [&results](const auto& ele)->void
                                                    {
                                                        results.emplace_back(ele.second);
                                                    });
    else
    {
        for(const auto& it: myMap)// binary_search; if not found add the value
            if(!std::binary_search(to_find.begin(), to_find.end(), it.first))
                results.emplace_back(it.second);
    }
 
    for(const auto& it: results) std::cout << it << std::endl;
}
 

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