LRU

class LRUCache {
public:
    list <pair <int , int>> cach ;
    int lim ;
    unordered_map <int , list <pair <int , int>> :: iterator> key_pointer;

    LRUCache(int capacity) {
        lim = capacity;

    }

    int get(int key) {

        if (key_pointer.count (key) == 0)
            return -1;

        list <pair <int , int>> :: iterator  it = key_pointer[key];

        int res = (*it).second;

        cach.push_front ( { (*it).first, (*it).second});
        key_pointer[key] = cach.begin();

        cach.erase(it);

        return res;
    }

    void put(int key, int value) {


        if (cach.size() == lim && key_pointer.count (key) == 0)
        {

            pair <int , int> to_remove = cach.back();

            key_pointer.erase(to_remove.first);

            cach.pop_back();

        }

        if (key_pointer.count (key) > 0)
        {
            list < pair < int ,int> > :: iterator it = key_pointer[key];
            cach.erase(it);

        }

        cach.push_front ({key, value});
        key_pointer[key] = cach.begin();

    }
};

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache* obj = new LRUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */

/*

head return
tail replaced
O(1) to get val

map <int, addres>

creat 1
head = 1 -> null
1 -> x
tail = 1

creat 2
head = 2 -> 1 -> head
2 -> y





*/