LRU设计

list是双向链表，map保存key对应到list中的迭代器的位置，list保存<key,value>

class LRUCache {
private:
	int c;
	map<int, list<pair<int, int>>::iterator> mymap;
	list<pair<int, int>> mylist;
public:
	
	LRUCache(int capacity) {
		// do intialization if necessary
		c = capacity;
	}

	 
	  int get(int key) {
		  // write your code here
		  if (mymap.count(key) == 0)
			  return -1;
		  list<pair<int, int>>::iterator it = mymap[key];
          int val= it->second;
    
		  mylist.erase(it);
		  mylist.push_front(pair<int, int>(key,val));
		  mymap[key] = mylist.begin();
		  return val;
	  }

	 
	  void put(int key, int value) {
		  // write your code here
		  if (mymap.count(key) == 0)
		  {
			  if (mymap.size() == c)
			  {
				  int tmpkey = mylist.back().first;
				  mylist.pop_back();
				  mymap.erase(tmpkey);
				 
			  }
			  mylist.push_front(pair<int, int>(key, value));
			  mymap[key] = mylist.begin();
		  }
		  else
		  {
			  list<pair<int, int>>::iterator it = mymap[key];
			  mylist.erase(it);
			  mylist.push_front(pair<int, int>(key, value));
			  mymap[key] = mylist.begin();
		  }
	  }
};