LRU cache实现

简单的链表实现

class LRUCache {private:    struct Node    {        Node *prev;        Node *next;        int key;        int value;        Node(int k,int v, Node* p = nullptr, Node *n = nullptr) :key(k),next(n), prev(p), value(v) {};    };public:    LRUCache(int capacity) {        maxCapacity = capacity;//最大容量        size = 0;//当前cache中的结点数量        head = nullptr;//头指针        tail = nullptr;//尾指针    }    //取出key的值    int get(int key) {        //看看key是否在map中,map存放的是key所在结点的指针        auto i = mapTable.find(key);        if (i == mapTable.end())            return -1;        else        {            //在map中,将node从原先位置删除,移动到头部            Node *node = (*i).second;            removeNode(node);            addNode(node);            return node->value;        }    }    void put(int key, int value) {        auto i = mapTable.find(key);        if (i == mapTable.end())        {            //检查是否超出容量            if (size == maxCapacity)            {                Node *tmp = tail;                removeNode(tail);                mapTable.erase(tmp->key);                delete tmp;            }            Node *node = new Node(key, value);            addNode(node);            mapTable[key] = node;        }        else        {            //在map中直接移动位置修改值即可            Node *node = (*i).second;            removeNode(node);            addNode(node);            node->value = value;        }    }private:    //添加node到头部    void addNode(Node *node)    {        if (head == nullptr)        {            head = node;            head->prev = nullptr;            tail = node;            tail->next = nullptr;        }        else        {            head->prev = node;            node->next = head;            node->prev = nullptr;            head = head->prev;        }        ++size;    }    //从把node从原先位置删除    void removeNode(Node *node)    {        if (node == head)        {            if (node->next == nullptr)            {                head = nullptr;                tail = nullptr;            }            else            {                head = head->next;                head->prev = nullptr;            }        }        else if (node == tail)        {            tail = tail->prev;            tail->next = nullptr;        }        else        {            node->prev->next = node->next;            node->next->prev = node->prev;        }        --size;    }private:    int maxCapacity;    int size;    Node *head;    Node *tail;    map<int, Node*> mapTable;};

LRUCache cache = new LRUCache( 2 /* capacity */ );cache.put(1, 1);cache.put(2, 2);cache.get(1);       // returns 1cache.put(3, 3);    // evicts key 2cache.get(2);       // returns -1 (not found)cache.put(4, 4);    // evicts key 1cache.get(1);       // returns -1 (not found)cache.get(3);       // returns 3cache.get(4);       // returns 4