LRU算法

 LRU算法：

#include<iostream>
#include<map>
 
using namespace std;
 
/**
 * Definition of cachelist node, it's double linked list node.
 */
struct CacheNode {
  int key;
  int value;
  CacheNode *pre, *next;
  CacheNode(int k, int v) : key(k), value(v), pre(NULL), next(NULL) {}
};
 
class LRUCache{
private:
  int size;                     // Maximum of cachelist size.
  CacheNode *head, *tail;
  map<int, CacheNode *> mp;          // Use hashmap to store
public:
  LRUCache(int capacity)
  {
    size = capacity;
    head = NULL;
    tail = NULL;
  }
 
  int get(int key)
  {
    map<int, CacheNode *>::iterator it = mp.find(key);
    if (it != mp.end())
    {
      CacheNode *node = it -> second;
      remove(node);
      setHead(node);
      return node -> value;
    }
    else
    {
      return -1;
    }
  }
 
  void set(int key, int value)
  {
    map<int, CacheNode *>::iterator it = mp.find(key);
    if (it != mp.end())
    {
      CacheNode *node = it -> second;
      node -> value = value;
      remove(node);
      setHead(node);
    }
    else
    {
      CacheNode *newNode = new CacheNode(key, value);
      if (mp.size() >= size)
      {
	map<int, CacheNode *>::iterator iter = mp.find(tail -> key);
      	remove(tail);
	mp.erase(iter);
      }
      setHead(newNode);
      mp[key] = newNode;
    }
  }
 
  void remove(CacheNode *node)
  {
    if (node -> pre != NULL)
    {
      node -> pre -> next = node -> next;
    }
    else
    {
      head = node -> next;
    }
    if (node -> next != NULL)
    {
      node -> next -> pre = node -> pre;
    }
    else
    {
      tail = node -> pre;
    }
  }
 
  void setHead(CacheNode *node)
  {
    node -> next = head;
    node -> pre = NULL;
 
    if (head != NULL)
    {
      head -> pre = node;
    }
    head = node;
    if (tail == NULL)
    {
      tail = head;
    }
  }
};
 
 
int main(int argc, char **argv)
{
  LRUCache *lruCache = new LRUCache(2);
  lruCache -> set(2, 1);
  lruCache -> set(1, 1);
  cout << lruCache -> get(2) << endl;
  lruCache -> set(4, 1);
  cout << lruCache -> get(1) << endl;
  cout << lruCache -> get(2) << endl;
}

力扣

146. LRU 缓存

请你设计并实现一个满足  LRU (最近最少使用) 缓存 约束的数据结构。

实现 LRUCache 类：

• LRUCache(int capacity) 以 正整数 作为容量 capacity 初始化 LRU 缓存
• int get(int key) 如果关键字 key 存在于缓存中，则返回关键字的值，否则返回 -1 。
• void put(int key, int value) 如果关键字 key 已经存在，则变更其数据值 value ；如果不存在，则向缓存中插入该组 key-value 。如果插入操作导致关键字数量超过 capacity ，则应该 逐出 最久未使用的关键字。

函数 get 和 put 必须以 O(1) 的平均时间复杂度运行。

示例：

输入
["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
[[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
输出
[null, null, null, 1, null, -1, null, -1, 3, 4]

解释
LRUCache lRUCache = new LRUCache(2);
lRUCache.put(1, 1); // 缓存是 {1=1}
lRUCache.put(2, 2); // 缓存是 {1=1, 2=2}
lRUCache.get(1);    // 返回 1
lRUCache.put(3, 3); // 该操作会使得关键字 2 作废，缓存是 {1=1, 3=3}
lRUCache.get(2);    // 返回 -1 (未找到)
lRUCache.put(4, 4); // 该操作会使得关键字 1 作废，缓存是 {4=4, 3=3}
lRUCache.get(1);    // 返回 -1 (未找到)
lRUCache.get(3);    // 返回 3
lRUCache.get(4);    // 返回 4

struct DLinkedNode{
    int key,value;
    DLinkedNode* prev;
    DLinkedNode* next;
    DLinkedNode():key(0),value(0),prev(nullptr),next(nullptr){}
    DLinkedNode(int _key,int _value):key(_key),value(_value),prev(nullptr),next(nullptr){}
};
class LRUCache {
public:
    LRUCache(int _capacity) {
        size=0;
        capacity=_capacity;
        head = new DLinkedNode();
        tail = new DLinkedNode();
        head->next=tail;
        tail->prev=head;
    }
    
    int get(int key) {
        if(!mp.count(key)){
            return -1;
        }

        DLinkedNode* node=mp[key];
        moveTohead(node);
        return node->value;
    }
    
    void put(int key, int value) {
        if(!mp.count(key)){
            DLinkedNode* node=new DLinkedNode(key,value);
            mp[key]=node;
            addToHead(node);
            ++size;
            if(size>capacity){
                DLinkedNode* removed=removeTail();
                mp.erase(removed->key);
                delete removed;
                --size;
            }
        }
        else{
            DLinkedNode* node=mp[key];
            node->value=value;
            moveTohead(node);
        }
    }
    void addToHead(DLinkedNode* node){
        node->prev=head;
        node->next=head->next;
        head->next->prev=node;
        head->next=node;
    }

    void removeNode(DLinkedNode*  node){
        node->prev->next=node->next;
        node->next->prev=node->prev;
    }

    void moveTohead(DLinkedNode* node){
        removeNode(node);
        addToHead(node);
    }

    DLinkedNode* removeTail(){
        DLinkedNode* node=tail->prev;
        removeNode(node);
        return node;
    }
private:
    unordered_map<int,DLinkedNode*> mp;
    int size;
    DLinkedNode* head;
    DLinkedNode* tail;
    int capacity;
};

/**
 * 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);
 */