LRU算法 c++手写 map

#include<iostream>
using namespace std;
#include<queue>
#include<map>
#include<string.h>



struct cachenode
{
    int key;
    int value;
    cachenode *pre;
    cachenode *next;
    cachenode(int key_t,int value_t)
    {
        key=key_t;
        value=value_t;
        pre=NULL;
        next=NULL;
    }
};

class lrucache
{
private:
    int lrucache_size;
    cachenode *head;
    cachenode *tail;
    map<int,cachenode*>mp;
public:
    lrucache(int size_tt)
    {
        lrucache_size=size_tt;
        head=NULL;
        tail=NULL;
    }
    void set_data(int key,int value)
    {
        map<int,cachenode*>::iterator it=mp.find(key);
        if(it!=mp.end())
        {
            cachenode *temp=it->second;
            temp->value=value;
            remove_data(temp);
            set_head(temp);
        }
        else
        {
            cachenode *new_node=new cachenode(key,value);
            if(mp.size()>=lrucache_size)
            {
                map<int,cachenode*>::iterator it=mp.find(tail->key);
                remove_data(tail);
                mp.erase(it);

            }
            set_head(new_node);
            mp[key]=new_node;
        }
    }
    int get_data(int key)
    {
        map<int,cachenode*>::iterator it=mp.find(key);
        if(it!=mp.end())
        {
            cachenode *temp=it->second;
            remove_data(temp);
            set_head(temp);
            return temp->value;
        }
        else
            return -1;
    }
    void remove_data(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 set_head(cachenode *node)
    {
        node->next=head;
        node->pre=NULL;
        if(head!=NULL)
        {
            head->pre=node;
        }
        head=node;
        if(tail==NULL)
            tail=head;

        //head=node;

    }

};

int main()
{
    lrucache *t_lrucache;
    t_lrucache=new lrucache(2);
    t_lrucache->set_data(2,1);
    t_lrucache->set_data(3,4);
    cout<<t_lrucache->get_data(3)<<endl;
    //cout<<"first"<<endl;
    t_lrucache->set_data(5,7);

    //cout<<"end"<<endl;
    cout<<t_lrucache->get_data(2)<<endl;
    cout<<t_lrucache->get_data(5)<<endl;
}