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class Node{
    public:
        int key;
        int val;
        Node* prev;
        Node* next;
 
        Node(int key,int val){
            this->key = key;
            this->val = val;
            prev = NULL;
            next = NULL;
        }
};
 
class LRUCache {
public:
 
    Node* head = new Node(-1,-1);
    Node* tail = new Node(-1,-1);
    int capacity;
    unordered_map<int,Node*> m;
 
    LRUCache(int _capacity) {
        capacity = _capacity;
        head->next = tail;
        tail->prev = head;
    }
    void addNode(Node* New){
        Node* temp = head->next;
        New->next = temp;
        New->prev = head;
        head->next = New;
        temp->prev = New;
    }
    void deleteNode(Node* del){
        Node* delprev = del->prev;
        Node* delnext = del->next;
        delprev->next = delnext;
        delnext->prev = delprev;
    }
 
 
 
    int get(int key) {
        if(m.find(key)!=m.end()){
            Node* resultNode = m[key];
            int ans = resultNode->val;
            m.erase(key);
            deleteNode(resultNode);
            addNode(resultNode);
            m[key] = head->next;
            return ans;
        }
        else return -1;
    }
 
    void put(int key, int value) {
       if(m.find(key)!=m.end()){
           Node* delNode = m[key];
           m.erase(key);
           deleteNode(delNode);
       }
        if(m.size()==capacity){
            m.erase(tail->prev->key);
            deleteNode(tail->prev);
        }
        Node* New = new Node(key,value);
        addNode(New);
        m[key] = head->next;
    }
};
 
/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache* obj = new LRUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */

prog.cpp: In constructor ‘Node::Node(int, int)’:
prog.cpp:11:20: error: ‘NULL’ was not declared in this scope
             prev = NULL;
                    ^~~~
prog.cpp:11:20: note: ‘NULL’ is defined in header ‘<cstddef>’; did you forget to ‘#include <cstddef>’?
prog.cpp:1:1:
+#include <cstddef>
 class Node{
prog.cpp:11:20:
             prev = NULL;
                    ^~~~
prog.cpp: At global scope:
prog.cpp:22:5: error: ‘unordered_map’ does not name a type
     unordered_map<int,Node*> m;
     ^~~~~~~~~~~~~
prog.cpp: In member function ‘int LRUCache::get(int)’:
prog.cpp:46:12: error: ‘m’ was not declared in this scope
         if(m.find(key)!=m.end()){
            ^
prog.cpp: In member function ‘void LRUCache::put(int, int)’:
prog.cpp:59:11: error: ‘m’ was not declared in this scope
        if(m.find(key)!=m.end()){
           ^
prog.cpp:64:12: error: ‘m’ was not declared in this scope
         if(m.size()==capacity){
            ^
prog.cpp:70:9: error: ‘m’ was not declared in this scope
         m[key] = head->next;
         ^

Standard output is empty