LRUCache Implementation using abstract class C++.

LRUCache.cpp

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

struct Node{
    Node *next,*prev;
    int key,value;
    Node(Node *p,Node *n, int k,int v):prev(p),next(n),key(k),value(v){};
    Node(int k,int v):prev(NULL),next(NULL),key(k),value(v){};
};

class Cache {
  protected:
  map<int,Node*> hash;
  int capacity;
  Node *front,*rear;

  virtual void set(int,int)=0;
  virtual int get(int)=0;
};

class LRUCache : Cache{
   public:
   LRUCache(int n){
       capacity=n;
       front=rear=NULL;
   }

   void set(int key,int value){
       Node *temp;
       if(hash.empty()){
          temp= new Node(key,value);
          front=rear=temp;
          hash[key]=temp;
          return;
       }else if (hash.find(key)==hash.end()){
            Node *N=new Node(front->prev,front,key,value);
            front->prev=N;
            front=N;
            hash[key]=N;
            if(hash.size()>capacity){
                rear=rear->prev;
                hash.erase(rear->next->key);
                free(rear->next);
                rear->next=NULL;
            }
            return;
       }else{
           hash[key]->value=value;
           
           if(hash[key]==front){
               return;
           }

           hash[key]->prev->next=hash[key]->next;

           if(rear==hash[key]){
               rear=rear->prev;
           }else{
               hash[key]->next->prev=hash[key]->prev;
           }

           hash[key]->next=front;
           hash[key]->prev=NULL;
           front->prev=hash[key];
           front=hash[key];
           return;
       }
        
   }

   int get(int key){
       if(hash.find(key)!=hash.end()){
         return hash[key]->value;
       }
       return -1;
   }
};

int main() {
  
   //dummy examples for input and output.
   int n, capacity,i;
   cin >> n >> capacity;
   LRUCache l(capacity);
   for(i=0;i<n;i++) {
      string command;
      cin >> command;
      if(command == "get") {
         int key;
         cin >> key;
         cout << l.get(key) << endl;
      } 
      else if(command == "set") {
         int key, value;
         cin >> key >> value;
         l.set(key,value);
      }
   }
   return 0;
}