leetcode[146]LRU Cache

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

struct CacheNode

{

    int key;

    int value;

    CacheNode(int k,int v):key(k),value(v){}

};

class LRUCache{

public:

    LRUCache(int capacity) {

        size=capacity;

    }

    

    int get(int key) {

        if(lmap.count(key))

        {

            auto iter=lmap[key];

            lis.splice(lis.begin(),lis,iter);

            lmap[key]=lis.begin();

            return lis.begin()->value;

        }

        else

            return -1;

    }

    

    void set(int key, int value) {

        if(lmap.count(key))

        {

            auto iter=lmap[key];

            lis.splice(lis.begin(),lis,iter);

            lis.begin()->value=value;

            lmap[key]=lis.begin();

            return;

        }

        else

        {

            if(lis.size()==size)

            {

               lmap.erase(lis.back().key);

               lis.pop_back();

               lis.push_front(CacheNode(key,value));

               lmap[key]=lis.begin();

            }

            else

            {

                lis.push_front(CacheNode(key,value));

                lmap[key]=lis.begin();

            }

            return;

        }

    }

private:

    int size;

    list<CacheNode> lis;

    unordered_map<int,list<CacheNode>::iterator> lmap;

};