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.

#include <list>

class LRUCache{
public:
    // @param capacity, an integer
    LRUCache(int capacity) {
        // write your code here
        this->capacity = capacity;
    }

    // @return an integer
    int get(int key) {
        // write your code here
        if (!hash.count(key)) {
            return -1;
        }
        cache.push_front(Node(key, hash[key]->val));
        cache.erase(hash[key]);
        hash[key] = cache.begin();
        return cache.front().val;
    }

    // @param key, an integer
    // @param value, an integer
    // @return nothing
    void set(int key, int value) {
        // write your code here
        if (hash.count(key)) {
            cache.erase(hash[key]);
        } else {
            if (cache.size() == capacity) {
                hash.erase(cache.back().key);
                cache.pop_back();
            }
        }
        cache.push_front(Node(key, value));
        hash[key] = cache.begin();
    }

    class Node {
    public:
        int key, val;
        Node(int _key, int _val) : key(_key), val(_val){}
    };

    int capacity;
    list<Node> cache;
    unordered_map<int, list<Node>::iterator> hash;
};