4. Multimap to Map

Point

---

1. return {};

요즘 Modern C++의 추세.

초기화된 객체를 반환.

반환 타입에 따라 빈 컨테이너, 기본값, 기본 생성자 호출이 이뤄짐

2. .find()는 기본적으로 iterator를 반환하며 iterator는 기본적으로 const

Problem

---

Your journey with std::multimap in C++ has equipped you with the skills to manipulate and traverse multiple key-value pairs efficiently. It's time to apply this knowledge! Imagine you're keeping track of participants' scores in a riveting quiz competition. Your task is to create a std::multimap in C++ to record these scores, possibly with multiple entries per participant. Then, write a function that aggregates all scores for each participant into a std::map, where each participant maps to a vector of scores they received. Your goal is to transform this multimap into a map, encapsulating all scores in a single vector for each participant.

For example, given the input multimap:

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{
    {"Olivia", 85},
    {"Liam", 92},
    {"Emma", 95},
    {"Noah", 90},
    {"Olivia", 88},
    {"Liam", 75},
    {"Emma", 89}
}
The output map should be:

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{
    {"Olivia", [85, 88]},
    {"Liam", [92, 75]},
    {"Emma", [95, 89]},
    {"Noah", [90]}
}
Embark on this challenge and effectively utilize std::multimap and std::map!

 

 

#include "solution.hpp"

std::map<std::string, std::vector<int>> aggregateScores(const std::multimap<std::string, int>& scores) {
    // TODO: Implement the aggregateScores function which takes a multimap of participant names (string) to scores (int)
    // and returns a map where each participant maps to a vector of their scores.
    
    std::map<std::string, std::vector<int>> map;
    
    for (const auto& score : scores) {
        // IsExist?
        auto it = map.find(score.first);
        if (it != map.end()) {
            // Exist
            it->second.push_back(score.second);
        } else {
            // Not Exist
            std::vector<int> number;
            number.push_back(score.second);
            map.emplace(std::make_pair(score.first, number));
        }
    }
    
    //return {};
    return map;
}

int main() {
    std::multimap<std::string, int> participantScores = {
        {"Olivia", 85},
        {"Liam", 92},
        {"Emma", 95},
        {"Noah", 90},
        {"Olivia", 88},
        {"Liam", 75},
        {"Emma", 89}
    };

    std::map<std::string, std::vector<int>> aggregatedScores = aggregateScores(participantScores);
    
    for (const auto& entry : aggregatedScores) {
        std::cout << "Participant: " << entry.first << " - Scores: ";
        for (int score : entry.second) {
            std::cout << score << " ";
        }
        std::cout << std::endl;
    }

    return 0;
}