keeper.cpp

/*
A class Keeper keeps a collection of numbers
The collection can be replaced by calling the update method with new numbers.
The method ends by detailing the changes made to the collection. (what remained the same, what was added, what was removed).
Output:
$ g++ --std=c++2a -fconcepts main.cpp && ./a.out 
New: 1 2 3 4.2 0 
Remaining: 
Deleted: 
Current: 0 1 2 3 4.2 
New: 8 10 
Remaining: 0 4.2 
Deleted: 1 2 3 
Current: 0 4.2 8 10 
*/

#include <iostream>
#include <set>
#include <vector>

template <typename T> class Keeper {
    private:
        std::set<T> numbers;
    public:
        void update(std::vector<T> nums) {
            std::set<T> nextNumbers;
            std::vector<T> added, remaining, removed;

            for(auto n : nums)
            {
                if(numbers.contains(n)) {
                    remaining.push_back(n);
                    nextNumbers.insert(n);
                    numbers.erase(n);
                } else {
                    added.push_back(n);
                    nextNumbers.insert(n);
                }
            }

            for(auto n: numbers) {
                removed.push_back(n);
            }

            numbers = nextNumbers;

            showIterable(added, "New: ");
            showIterable(remaining, "Remaining: ");
            showIterable(removed, "Deleted: ");
            showIterable(numbers, "Current: ");
        }

        void showIterable( auto v, std::string str) {
            std::cout << str;
            for(auto n: v) {
                std::cout << n << " ";
            }
            std::cout << std::endl;
        }
};

int main() {
    Keeper<float> k;

    std::cout << std::endl;
    k.update( {1, 2, 3, 4.2, 0});
    std::cout << std::endl;
    k.update( {0,4.2,8,10});

    return 0;    
}