CareerCup

In Java, we can do it using LinkedHashMap

public LRUCache(final int size) {
		this.size = size;

		cache = new LinkedHashMap<K,V>(size, 0.75f, true) {
			//Return true when LinkedHashMap should delete its eldest
			//entry
			protected boolean removeEldestEntry(Map.Entry eldest) {
				return size() > size;

			}
		};
	}

C++ Code (Queue with DLL and Hash Map)

struct LRUCacheNode {
		int key;
		int value;
		LRUCacheNode* prev;
		LRUCacheNode* next;
		LRUCacheNode(): key(0),value(0),next(NULL),prev(NULL) { } ;
} ;

class LRUCache{
private:
    hash_map< int, LRUCacheNode* >  Map;
    LRUCacheNode *  Head;
    LRUCacheNode *  Tail;
	int Capacity ;
	int Count ;
    
public:
    LRUCache(int capacity) {
		Capacity = capacity ;
		Count = 0 ;
        Head = new LRUCacheNode;
        Tail = new LRUCacheNode;
        Head->prev = NULL;
        Head->next = Tail;
        Tail->next = NULL;
        Tail->prev = Head;
    }
    
    ~LRUCache ( ) {
        delete Head;
        delete Tail;
    }
    
    int get(int key) {
        LRUCacheNode* node = Map[key];
        if(node)
        {
            DetachNode(node);
            AttachNodeToFront(node);
            return node->value;
        }
        else
        return -1 ;

    }
    
    void set(int key, int value) {
        LRUCacheNode* node = Map[key];
        if(node)
        {
            DetachNode(node);
            node->value = value;
            AttachNodeToFront(node);
        }
        else{
			LRUCacheNode* node = new LRUCacheNode ;
            if ( Capacity == Count ) { // If Cache is Full
                RemoveLRUNode ( key ) ;					
            }
            
			node->key = key;
			node->value = value;
			Map[key] = node;
			AttachNodeToFront(node);
			Count++ ;            
        }
    }
private:
	void RemoveLRUNode ( int key ) {
		LRUCacheNode* node = Tail->prev;
        DetachNode(node);
        Map.erase(node->key);
		Count-- ;
	}

    void DetachNode(LRUCacheNode* node) {
            node->prev->next = node->next;
            node->next->prev = node->prev;
    }
    
    void AttachNodeToFront(LRUCacheNode* node) {
            node->next = Head->next;
            node->prev = Head;
            Head->next = node;
            node->next->prev = node;
    }
};