LRU（找工作之路，漫漫其修远兮）

struct DList {
    int key, value;
    DList *next, *pre;

    DList() : key(0), value(0), next(nullptr), pre(nullptr) {}

    DList(int _key, int _value) : key(_key), value(_value), next(nullptr), pre(nullptr) {}
};

class LRUCache {
private:
    int cap, nowSize = 0;
    map<int, DList *> mp;
    DList *head;
    DList *tail;

    void move_to_head(DList *node) {
        remove(node);
        add_to_head(node);
    }

    void remove(DList *node) {
        DList *Pre = node->pre;
        DList *Next = node->next;
        Pre->next = Next;
        Next->pre = Pre;
    }

    void add_to_head(DList *node) {
        DList *Sec = head->next;
        Sec->pre = node;
        node->next = Sec;
        head->next = node;
        node->pre = head;
    }

public:
    LRUCache(int capacity) {
        mp.clear();
        cap = capacity;
        head = new DList();
        tail = new DList();
        head->next = tail;
        tail->pre = head;
    }

    int get(int key) {
        if (!mp.count(key)) {
            return -1;
        } else {
            DList *node = mp[key];
            move_to_head(node);
            return node->value;
        }
    }

    void put(int key, int value) {
        if (!mp.count(key)) {
            DList *node = new DList(key, value);
            add_to_head(node);
            nowSize++;
            mp[key] = node;
            if (nowSize > cap) {
                mp.erase(tail->pre->key);
                remove(tail->pre);
                nowSize--;
            }
        } else {
            DList *node = mp[key];
            node->value = value;
            move_to_head(node);
        }
    }
};

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache* obj = new LRUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */

对封装的一些见解