左神算法学习日记——LRU数据结构设计

template <typename K,typename V>
class Node
{
public:
	K key;
	V value;
	Node<K, V>* next;
	Node<K, V>* last;
	Node() = default;
	Node(K k, V v)
	{
		key = k;
		value = v;
		next = NULL;
		last = NULL;
	}
};

template <class K,class V>
class List
{
public:
	Node<K, V>* head;
	Node<K, V>* end;
	void addNode(Node<K, V>* node)
	{
		if (!node)
			return;
		if (!head)
		{
			head = node;
			end = node;
		}
		else
		{
			end->next = node;
			node->last = end;
			end = node;
		}
	}
	void removehead()
	{
		if (!head)
			return;
		Node<K, V> temp = head;
		head = head->next;
		delete temp;
	}
	void moveToend(Node<K, V>* node)
	{
		if (!node || node == end)
			return;
		if (node == head)
			node->next->last = NULL;
		else
		{
			node->last->next = node->next;
			node->next->last = node->last;
		}
		node->last = end;
		node->next = NULL;
		end->next = node;
		end = node;
	}
	~List()
	{
		while (end)
		{
			Node<K, V> temp = head;
			head = head->next;
			delete temp;
		}
	}
};

template<class K,class V>
class LRU
{
public:
	List<K, V> L;//只有双端队列可以实现优先级更新，单链表不得行
	hash_map<K, Node<K,V>*> map;//利用hash表实现随机存取
	int Size;
	LRU() = default;
	LRU(int size)
	{
		Size = size;
	}
	void set(K key, V value)
	{
		if (map.find(key) == map.end())
		{
			Node<K, V>* node = new Node<K, V>(key, value);
			map.insert(make_pair<K,V>(key,node));
			L.addNode(node);//更新hash表的同时，更新双端队列
			if (map.size() > Size)//元素数量超过空间限制时删除LRU元素
			{
				map.erase(L.head);
				L.removehead();
			}
		}
		else
		{
			map[key]->value = value;
			L.moveToend(map[key]);//更新优先级
		}
	}
	V get(K key)
	{
		if (map.find(key) == map.end())
			return NULL;
		L.moveToend(map[key]);//更新优先级
		return map[key]->value;
	}
};