Custom cache

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

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

    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;
        }
        addresses[key]->next->prev = 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;
        }
        auto node = new Node(value);
        addresses[key] = node;
        if (!begin || !end) {
            begin = end = node;
        } else {
            node->prev = begin;
            begin->next = node;
            begin = node;
            end->next->prev = nullptr;
            end = end->next;
        }
    }
};