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;
};