LRU Cache

Problem

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.

Solution

class LRUCache{
    struct Node{
        Node(int k, int v) : key(k), value(v){}
      int key;
      int value;
    };
    int cap;
    int size;
    list<Node> m_list;
    unordered_map<int, list<Node>::iterator> mp;
    
public:
    LRUCache(int capacity):cap(capacity),size(0) {
        
    }
    
    int get(int key) {
        if(mp.find(key) == mp.end()) return -1;
        
        auto pos = mp[key];
        int val = pos->value;
        
        m_list.erase(pos);
        m_list.push_front(Node(key,val));
        mp[key] = m_list.begin();
        return val;
    }
    
    void set(int key, int value) {
        auto pos = mp.find(key);
        // Not in cache
        if(pos == mp.end()) {
            if(size >= cap) {
                int k = (m_list.back()).key;
                mp.erase(k);
                m_list.pop_back();
            }
            else {
                size++;
            }
            m_list.push_front(Node(key,value));
        }
        // in cache
        else {
            m_list.erase(mp[key]);
            m_list.push_front(Node(key,value));
        }
        mp[key] = m_list.begin();
    }
};