c.cpp

#include<map>
#include <string>

class Person {
public:
    void ChangeFirstName(int year, const std::string &first_name) {
        firstNameCache[year] = first_name;
        firstChanged = true;
    }

    void ChangeLastName(int year, const std::string &last_name) {
        lastNameCache[year] = last_name;
        secondChanged = true;
    }

    std::string GetFullName(int year) {
        std::string out;
        if (!firstChanged and !secondChanged) {
            out = "Incognito";
        } else if (!firstChanged) {
            out = getEarliest(lastNameCache, year) + " with unknown first name";
        } else if (!secondChanged) {
            out = getEarliest(firstNameCache, year) + " with unknown last name";
        } else {
            out = getEarliest(firstNameCache, year) + " " + getEarliest(lastNameCache, year);
        }
        return out;
    }

private:
    std::string getEarliest(std::map<int, std::string> &m, int year) {
        int currentInt = -1;
        std::string out;
        for (const auto &elem : m) {
            if (elem.first <= year && elem.first > currentInt) {
                currentInt = elem.first;
                out = elem.second;
            }
        }
        return out;
    }

    bool firstChanged = false;
    bool secondChanged = false;
    std::map<int, std::string> firstNameCache;
    std::map<int, std::string> lastNameCache;
};