solution.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() ) 
        {

            N = new Node(k,v);
            tail = head = N;
            mp[k] = N;

            return;
        }
        auto it = mp.find(k);
        if ( it != mp.end() ) 
        {
            it->second->value = v;
            if ( head == it->second ) 
            {
                return;
            }
            it->second->prev->next = it->second->next;           
            if ( tail == it->second ) 
            {
                tail = tail->prev;
            }
            else 
            {               
                it->second->next->prev = it->second->prev;
            }           
            it->second->next = head;
            it->second->prev = nullptr;
            head->prev = it->second;
            head = it->second;
        }
        else 
        {
            N = new Node(head->prev, head, k, v);
            head->prev = N; 
            head = N;
            mp[k] = N;
            if ( mp.size() > cp ) 
            {
                tail = tail->prev;
                mp.erase(tail->next->key);
                delete tail->next; 
                tail->next = nullptr;
            }
        }
    }
    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;
}