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/*

* LRU cache

*

* because need to move the entry around, thus double-linked list is a good fit

*

* head of the list: most recently visited data

* tail of the list: least recently visited data

*

* // NOTE: !!! still broken, but the idea is right!

*

*/

#include <iostream>

#include <unordered_map>

using namespace std;

typedef struct node {

void *data;

struct node* prev;

struct node* next;

} Node;

Node *head = NULL;

const int CACHE_SIZE = 3;

unordered_map<int, Node*> hashmap;

int size = 0;

void insert_front(Node*& head, void* data);

void remove_tail(Node*& head);

void free_double_list(Node* head);

void print_double_list(Node* head);

void print_node(Node* p);

bool isListFull(Node* head);

void move_to_front(Node*& head, Node* p);

void set(int key, void* data)

{

Node *p = hashmap[key];

if(p==NULL) {

insert_front(head, data);

hashmap[key] = head;

} else {

p->data = data;

move_to_front(head, p);

hashmap[key] = head;

}

}

void* get(int key)

{

// update hash table

Node* p = hashmap[key];

// move the just visited node to the front

move_to_front(head, p);

return p;

}

void move_to_front(Node*& head, Node* p)

{

if (p==NULL || head==NULL)

return;

if(p==head) { // alreay in front

return;

}

Node* prev = p->prev;

Node* next = p->next;

prev->next = next;

next->prev = prev;

p->next = head;

p->prev = NULL;

head = p;

}

void insert_front(Node*& head, void* data)

{

Node* p = new Node;

p->data = data;

p->prev = NULL;

p->next = NULL;

if(head==NULL) {

head = p;

return;

}

if (isListFull(head)) {

remove_tail(head);

//update hash table

}

p->next = head;

head->prev = p;

head = p;

}

bool isListFull(Node* head)

{

int len = 0;

while(head!=NULL) {

len++;

head = head->next;

}

if (len == CACHE_SIZE)

return true;

else

return false;

}

void remove_tail(Node*& head)

{

if (head==NULL) {

return;

}

// only one node (head)

if (head->next == NULL) {

delete head;

head = NULL;

return;

}

Node* tail = head;

while(tail->next) {

tail = tail->next;

}

Node* new_tail = tail->prev;

if(new_tail) {

new_tail->next = NULL;

}

//update hash table

int key = *(int*)tail->data;

cout << "remove key: " << key << endl;

hashmap[key] = NULL;

delete tail;

}

void free_double_list(Node* head)

{

if (head==NULL)

return;

Node* to_delete = head;

Node* p = to_delete->next;

while(p!=NULL) {

delete to_delete;

to_delete = p;

if (p->next==NULL) { // tail of the list; done

return;

}

p = p->next;

}

}

void print_node(Node* p)

{

if (p!=NULL) {

cout << *(int*)(p->data) << " ";

}

}

void print_double_list(Node* head)

{

while(head!=NULL) {

print_node(head);

head = head->next;

}

cout << endl;

}

int main()

{

int a[] = {2,3,7,3,5,2};

//int a[] = {2};

int len = sizeof(a)/sizeof(a[0]);

for(int i=0; i<len; i++) {

set(a[i], &a[i]);

print_double_list(head);

}

free_double_list(head);

return 0;

}