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.

class LRUCache{
public:
    LRUCache(int capacity) 
    {
         m_cache.clear();
         m_time2key.clear();
         m_key2time.clear();
         m_capacity = capacity;
         m_time = 0;
         m_size = 0;
    }

    int get(int key)
    {
        m_time ++;
        map<int, int >
 
::iterator it = m_cache.find(key);
        if(it != m_cache.end() )
        {
            m_time2key.erase(m_key2time[key]);
            m_time2key.insert(std::make_pair(m_time, key));
            m_key2time[key] = m_time;
            return m_cache[key];
        }

        return -1;
    }

    void
 
 set(int key, int value) 
    {
        m_time++;

        map<int, int >::iterator it = m_cache.find(key);
        if(it != m_cache.end())
        {
            m_cache[key] = value;
            m_time2key.insert(std::make_pair(m_time, key));
            m_time2key.erase(m_key2time[key]);
            m_key2time[key] = m_time;
        }
        else
        {
            if(m_size == m_capacity)
            {
                map<long long, int>::iterator it = m_time2key.begin();
                m_cache.erase(it->second);
                m_time2key.erase(it->first);
                m_key2time.erase(it->second);
                m_size--;
            }
            m_cache.insert(std::make_pair(key, value));
            m_time2key.insert(std::make_pair(m_time, key));
            m_key2time.insert(std::make_pair(key, m_time));
            m_size++;
        }
    }
private:
    map<int, int > m_cache;
    long long m_time;
    map<long long, int> m_time2key;
    map<int, long long> m_key2time;
    int m_capacity;
    int m_size;
};