C++ を使用して効率的な推奨アルゴリズムを開発するにはどうすればよいですか?

UserID, ItemID, Rating
1, 1, 5
1, 2, 4
2, 1, 3
2, 3, 5
3, 2, 2

#include <iostream>
#include <fstream>
#include <vector>

std::vector<std::vector<int>> loadData(const std::string& filename) {
    std::ifstream file(filename);
    std::string line;
    std::vector<std::vector<int>> data;
    
    while (std::getline(file, line)) {
        std::vector<int> record;
        std::istringstream iss(line);
        std::string token;
        
        while (std::getline(iss, token, ',')) {
            record.push_back(std::stoi(token));
        }
        
        data.push_back(record);
    }
    
    return data;
}

#include <iostream>
#include <vector>
#include <unordered_map>

std::unordered_map<int, std::vector<int>> userBasedCF(const std::vector<std::vector<int>>& data, int userId) {
    std::unordered_map<int, std::vector<int>> similarUsers;
    
    // 计算用户之间的相似度（这里使用简单的余弦相似度）
    for (const auto& record1 : data) {
        int user1 = record1[0];
        int item1 = record1[1];
        
        if (user1 != userId) {
            for (const auto& record2 : data) {
                int user2 = record2[0];
                int item2 = record2[1];
                
                if (user2 != userId && item1 == item2) {
                    similarUsers[user1].push_back(user2);
                }
            }
        }
    }
    
    return similarUsers;
}

int main() {
    std::vector<std::vector<int>> data = loadData("data.txt");
    int userId = 1;
    
    std::unordered_map<int, std::vector<int>> similarUsers = userBasedCF(data, userId);
    
    for (const auto& p : similarUsers) {
        std::cout << "User " << p.first << ": ";
        
        for (const auto& id : p.second) {
            std::cout << id << " ";
        }
        
        std::cout << std::endl;
    }
    
    return 0;
}