AbstractClassesPolymorphism.cpp

#include <iostream>
#include <vector>
#include <map>
#include <string>
#include <algorithm>
#include <set>
#include <cassert>
using namespace std;

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

class Cache{
   
   protected: 
   map<int,Node*> mp; //map the key to the node in the linked list
   int cp;  //capacity
   Node* tail; // double linked list tail pointer
   Node* head; // double linked list head pointer
   virtual void set(int, int) = 0; //set function
   virtual int get(int) = 0; //get function

};
class LRUCache : public Cache {
public:
  LRUCache(int c) { cp = c; }

  void set(int k, int v) {
    Node *N;

    if (mp.empty()) // No nodes
    {
      N = new Node(k, v);
      tail = head = N;
      mp[k] = N;

      return;
    }

    auto it = mp.find(k);

    if (it != mp.end()) // In hash table
    {
      it->second->value = v; // update value

      if (head == it->second) // head?
        return;

      it->second->prev->next = it->second->next;

      if (tail == it->second) // tail?
        tail = tail->prev;
      else // in between?
        it->second->next->prev = it->second->prev;

      it->second->next = head;
      it->second->prev = NULL;
      head->prev = it->second;
      head = it->second;
    } else // No in hash table
    {
      N = new Node(head->prev, head, k, v); // new node
      head->prev = N;
      head = N;
      mp[k] = N;

      if (mp.size() > cp) // capacity?
      {
        tail = tail->prev;
        mp.erase(tail->next->key);
        delete tail->next;
        tail->next = NULL;
      }
    }
  }

  int get(int k) {
    auto it = mp.find(k);
    if (it != mp.end())
      return it->second->value;

    return -1;
  }
};
int main() {
   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;
}