#include <unordered_set>
    #include <vector>
    #include <iostream>
    
    int main()
    {
       std::unordered_set<int> tempSet;
       std::vector<int> vec { 55, 55, 55, 1, 23, 45 };
       for ( auto& val : vec )
       {
          if (!tempSet.count(val)) 
             std::cout << val << " "; 
          tempSet.insert(val); 
       }
    }