#include <iostream>#include <string>#include <vector>#include <unordered_map>using namespace std;template<typename K, typename T>struct LRUCacheEntry{    K key;    T data;    LRUCacheEntry* prev;    LRUCacheEntry* next;};template<typename K, typename T>class LRUCache{    private:        unordered_map<K, LRUCacheEntry<K, T>*> _mapping;        vector< LRUCacheEntry<K, T>* >         _freeEntries;        LRUCacheEntry<K, T> *                  head;        LRUCacheEntry<K, T> *                  tail;        LRUCacheEntry<K, T> *                  entries;    public:        LRUCache(size_t size)        {            entries = new LRUCacheEntry<K, T>[size];            for(int i = 0; i < size; i++ )            _freeEntries.push_back(entries + i );            head = new LRUCacheEntry<K, T>;            tail = new LRUCacheEntry<K, T>;            head->prev = NULL;            head->next = tail;            tail->next = NULL;            tail->prev = head;        }        ~LRUCache()        {            delete head;            delete tail;            delete [] entries;        }        void put(K key, T data)        {            LRUCacheEntry<K, T>* node = _mapping[key];            if(node)            {                detach(node);                node->data = http://www.mamicode.com/data;"";        }    private:        void detach(LRUCacheEntry<K, T>* node)        {            node->prev->next = node->next;            node->next->prev = node->prev;        }        void attach(LRUCacheEntry<K, T>* node)        {            node->next = head->next;            node->prev = head;            head->next = node;            node->next->prev = node;        }};int main(int argc, const char *argv[]){  unordered_map<int, int> map_;  map_[9] = 999;  cout << map_[9] << endl;  cout << map_[10] << endl;  LRUCache<int ,string> lru_cache(100);  lru_cache.put(1, "one");  cout << lru_cache.get(1) << endl;  if(lru_cache.get(2) == "")      lru_cache.put(2, "two");  cout << lru_cache.get(2) << endl;    return 0;}