LRU Cache

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

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(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.

The cache is initialized with a positive capacity.

Follow up:
Could you do both operations in O(1) time complexity?

Example:

LRUCache cache = new LRUCache( 2 /* capacity */ );

cache.put(1, 1);
cache.put(2, 2);
cache.get(1);       // returns 1
cache.put(3, 3);    // evicts key 2
cache.get(2);       // returns -1 (not found)
cache.put(4, 4);    // evicts key 1
cache.get(1);       // returns -1 (not found)
cache.get(3);       // returns 3
cache.get(4);       // returns 4

class LRUCache {
    private:
    list<pair<int, int>> lst;
    unordered_map<int, list<pair<int, int>>::iterator> mp;
    int cap;
    
    void makeHot(list<pair<int, int>>::iterator it) {
            pair<int, int> data = *it;
            lst.erase(it);
            
            lst.push_front(data);
            mp[data.first] = lst.begin();
    }
public:
    LRUCache(int capacity) {
        cap = capacity;
    }
    
    int get(int key) {
        if (mp.find(key) == mp.end()) {
            return -1;
        }

        int val = (*mp[key]).second;
        makeHot(mp[key]);
        return val;
    }
    
    void put(int key, int value) {
        if (mp.find(key) != mp.end()) {
            lst.erase(mp[key]);
        } else if (lst.size() == cap && cap >= 1) {
            int key = lst.back().first;
            lst.pop_back();
            mp.erase(key);
        }

        lst.push_front(make_pair(key, value));
        mp[key] = lst.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);
 */