Custom cache

#include <iostream>
#include <unordered_map>
#include <string>

template<typename T, typename U>
struct custom_cache{
    struct Node {
        Node() = default;
        Node(T key, U value) : key(key), value(value) {}
        T key;
        U value;
        Node* next = nullptr;
        Node* prev = nullptr;
    };

    unsigned int N = 0;
    unsigned int amount = 0;
    custom_cache(unsigned int N) : N(N) {}

    std::unordered_map<T, Node*> addresses;
    Node* begin = nullptr;
    Node* end = nullptr;

    U get(T key) {
        if (!begin || !end || addresses.count(key) == 0) {
            return NULL;
        }
        if (addresses[key]->next) {
            addresses[key]->next->prev = addresses[key]->prev;
        }
        if (addresses[key]->prev) {
            addresses[key]->prev->next = addresses[key]->next;
        }
        begin->next = addresses[key];
        addresses[key]->next = nullptr;
        addresses[key]->prev = begin;
        begin = addresses[key];
        return begin->value;
    }

    void put(T key, U value) {
        if (addresses.count(key) != 0) {
            return;
        }
        amount++;
        auto node = new Node(key, value);
        addresses[key] = node;
        if (!begin || !end) {
            begin = end = node;
        } else {
            node->prev = begin;
            begin->next = node;
            begin = node;
            if (amount > N) {
                amount = N;
                addresses[end->key] = end->next->prev = nullptr;
                delete end->next->prev;
                end = end->next;
            }
        }
    }

    void printList() {
        auto node = begin;
        while (node) {
            std::cout << node->key << ' ' << node->value << '\n';
            node = node->prev;
        }
    }
};

void getAll(custom_cache<int, std::string>* cache) {
    std::cout << cache->get(3) << ' ';
    std::cout << cache->get(4) << ' ';
    std::cout << cache->get(5) << '\n';
}

void test1() {
    int a = 3, b = 4, c = 5;
    std::string s1 = "a", s2 = "b", s3 = "c";
    auto cache = custom_cache<int, std::string>(3);
    cache.put(a, s1);
    cache.put(b, s2);
    cache.put(c, s3);
    getAll(&cache);
    cache.printList();
}

void test2() {
    int a = 3, b = 4, c = 5;
    std::string s1 = "a", s2 = "b", s3 = "c";
    auto cache = custom_cache<int, std::string>(2);
    cache.put(a, s1);
    cache.put(b, s2);
    cache.put(c, s3);
    cache.printList();
}

void test3() {
    int a = 3, b = 4, c = 5;
    std::string s1 = "a", s2 = "b", s3 = "c";
    auto cache = custom_cache<int, std::string>(1);
    cache.put(a, s1);
    cache.put(b, s2);
    cache.put(c, s3);
    cache.printList();
}

int main() {
    test1();
    std::cout << "\n\n";
    test2();
    std::cout << "\n\n";
    test3();
}