146. LRU Cache

class LRUCache {
public:
    list<pair<int,int>> q;
    unordered_map<int,list<pair<int,int>>::iterator> m;
    int cap;
    LRUCache(int capacity) {
        cap = capacity;
    }
    
    int get(int key) {
        if (!m.count(key))  return -1;
        auto it = m[key];
        int val = it->second;
        q.erase(it);
        q.push_front({key,val});
        m[key] = q.begin();
        return val;
    }
    
    void put(int key, int value) {
        if (m.count(key)) {
            auto it = m[key];
            q.erase(it);
            q.push_front({key,value});
            m[key] = q.begin();
            return;
        }
        if (m.size() == cap) {
            auto it = q.rbegin();
            int delete_key = it->first;
            q.pop_back();
            m.erase(delete_key);
        }
        q.push_front({key,value});
        m[key] = q.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);
 */