Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.
get(key) – Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) – Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item
class LRUCache{ //define the double linked list, each node stores both the key and value.
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){};
};
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
public:
//constructor
LRUCache(int capacity) {
cp = capacity;
mp.clear();
head=NULL;
tail=NULL;
}
//insert node to the tail of the linked list
void insertNode(Node* node){
if (!head){
head = node;
tail = node;
}else{
tail->next = node;
node->prev = tail;
tail = tail->next;
}
}
//remove current node
void rmNode(Node* node){
if (node==head){
head = head->next;
if (head){head->prev = NULL;}
}else{
if (node==tail){
tail =tail->prev;
tail->next = NULL;
}else{
node->next->prev = node->prev;
node->prev->next = node->next;
}
}
}
// move current node to the tail of the linked list
void moveNode(Node* node){
if (tail==node){
return;
}else{
if (node==head){
node->next->prev = NULL;
head = node->next;
tail->next = node;
node->prev = tail;
tail=tail->next;
}else{
node->prev->next = node->next;
node->next->prev = node->prev;
tail->next = node;
node->prev = tail;
tail=tail->next;
}
}
}
///////////////////////////////////////////////////////////////////////
// get method
///////////////////////////////////////////////////////////////////////
int get(int key) {
if (mp.find(key)==mp.end()){
return -1;
}else{
Node *tmp = mp[key];
moveNode(tmp);
return mp[key]->value;
}
}
///////////////////////////////////////////////////////////////////////
// set method
///////////////////////////////////////////////////////////////////////
void set(int key, int value) {
if (mp.find(key)!=mp.end()){
moveNode(mp[key]);
mp[key]->value = value;
}else{
if (mp.size()==cp){
mp.erase(head->key);
rmNode(head);
}
Node * node = new Node(key,value);
mp[key] = node;
insertNode(node);
}
}
};
Runtime: 376 ms