LRU

最新推荐文章于 2025-09-03 19:44:06 发布

转载最新推荐文章于 2025-09-03 19:44:06 发布 · 51 阅读

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原文链接：https://my.oschina.net/lvyi/blog/346227

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#数据结构与算法

为什么80%的码农都做不了架构师？>>>

LRU是Least Recently Used算法的简称，在linux的内存页框管理里面用到。LeetCode上排名第一的就是这个算法。

有一个cache，大小固定，采用双向链表存储，哈希表用来检索。当有数据时，放到链表尾。如果大小溢出，则删除头节点。

读取链表中的数据，有的话则返回值，同时将该数据的节点放置在尾结点。

##Code##

<!-- lang: cpp -->
struct LRUStruct
{
int key;
int value;
LRUStruct *pre;
LRUStruct *next;
LRUStruct(int k=0,int v=0,LRUStruct *p=NULL,LRUStruct *n=NULL):key(k),value(v),pre(p),next(n){}
};
struct HeadTail
{
LRUStruct head;
LRUStruct tail;
HeadTail(LRUStruct h,LRUStruct t):head(h),tail(t){}
};

class LRUCache{
public:
int size;
unordered_map<int,LRUStruct*> keyMap;
HeadTail ht;

LRUCache(int capacity):ht(LRUStruct(),LRUStruct())
{
    size=capacity;
}

int get(int key) {
    if((keyMap.empty()) || (!keyMap.count(key))) return -1;
    LRUStruct *ls=keyMap[key];
    ls->pre->next=ls->next;
    ls->next->pre=ls->pre;
    insertTail(ls);
    return ls->value;
}


void set(int key, int value) {
    if (keyMap.empty())
    {
        LRUStruct *ls=new LRUStruct(key,value);
        ht.head.next=ls;
        ls->pre=&ht.head;
        ht.tail.pre=ls;
        ls->next=&ht.tail;
        keyMap[key]=ls;
        return;
    }
    if (keyMap.count(key))
    {
        LRUStruct *ls=keyMap[key];
        ls->value=value;
        ls->pre->next=ls->next;
        ls->next->pre=ls->pre;
        insertTail(ls);
    }
    
    else
    {
        if(keyMap.size()<size)
        {
            LRUStruct *ls=new LRUStruct(key,value);
            insertTail(ls);
            keyMap[key]=ls;
        }
        else
        {
            LRUStruct *p_tmp = ht.head.next;
            keyMap.erase(p_tmp->key);
            deleteHead();

            LRUStruct *ls = new LRUStruct(key,value);
            insertTail(ls);

            keyMap[key] = ls;
            delete p_tmp;
        }
    }
    
}

   void insertTail(LRUStruct *ls)
   {
       ls->pre=ht.tail.pre;
       ht.tail.pre->next=ls;
       ls->next=&ht.tail;
       ht.tail.pre=ls;
       
   }
   
   void deleteHead()
   {
       ht.head.next=ht.head.next->next;
       ht.head.next->pre=&ht.head;
       
   }
 };

##Reference##

[1].http://blog.youkuaiyun.com/beiyeqingteng/article/details/7010411

[2].http://blog.youkuaiyun.com/zqpgood/article/details/6781195

[3].http://www.2cto.com/kf/201401/274774.html

转载于:https://my.oschina.net/lvyi/blog/346227