LRU cache

/*
Time complexity :complexity of erase only
we created a cache list of pair which will keep key and value pairs and we are keeping address of that pair of cache ie. list in map
whose key will be actual key of that pair.
we will keep our cache as most recent accesed element at front and least recent accessed element at back of cache.
refreshposition will adjust position of an internal node in cache ie. node that is not in front nor in back to front.
*/

class LRUCache{
    private:
      list<pair<int,int>> cache;
      unordered_map<int,list<pair<int,int>>::iterator> mymap;  //Key, address in cache array ie. our cache memory
      int capacity;

    public:
    void refreshPosition(int key,int value){
        cache.erase(mymap[key]);
        cache.push_front(make_pair(key,value));
        mymap[key] = cache.begin();     //Addr of new position stored in map
    }


    LRUCache(int cap){
       this->capacity = cap;
    }

    int get(int key){
        if(mymap.find(key)!=mymap.end()){
            refreshPosition(key,(*mymap[key]).second);  //just because it has been hit,so it's most recently used so updation.here start is used because
                                                        //mymap[key] gives the addresss of that pair,and * at begining means that pair.
            return (*mymap[key]).second;                //returning value for the key
        }
        return -1;
    }

    void set(int key, int value){
        if(mymap.find(key)!=mymap.end())
            refreshPosition(key,value);               //if present in the cache,then updating the position to front of the cache
        else{                                         //if not present in cache,then adding it into cache and at the front of the cache
            cache.push_front(make_pair(key,value));
            mymap[key] = cache.begin();
            if(mymap.size()>capacity){                //if capacity exceeds,removing element from the back.
                mymap.erase(cache.back().first);
                cache.pop_back();
            }
        }
    }
};