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使用循环链表实现LRU算法

使用循环链表实现LRU算法

C++ 写法

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    struct node{
int key;
int value;
struct node * left;
struct node * right;
node(int k,int v){
key = k;
value = v;
left = NULL;
right = NULL;
}
};

class LRUCache {
public:

struct node * head;
struct node * tail;
int capacity = 0;
int current_size = 0;

LRUCache(int capacity) {
this->capacity = capacity;
head = new node(0,0);
tail = new node(0,0);
head -> left = tail;
head -> right = tail;
tail -> left = head;
tail -> right = head;
}

int get(int key) {
struct node * ptr = head -> right;
while (ptr != NULL && ptr != tail) {
if( ptr -> key == key ){
int value = ptr->value;
delete_node(ptr);
ptr = new node(key,value);
add_to_head(ptr);
return value;
}
ptr = ptr -> right;
}
return -1;
}

void put(int key, int value) {
struct node * ptr = head->right;
bool exists = false;
if( current_size > 0){
while (ptr != NULL && ptr != tail) {
if( ptr -> key == key ){
delete_node(ptr);
ptr = new node(key,value);
add_to_head(ptr);
exists = true;
break;
}
ptr = ptr -> right;
}
}
if(!exists){
if( current_size < capacity ){
current_size ++;
}else{
delete_tail();
}
ptr = new node(key,value);
add_to_head(ptr);
}
}

private:

void delete_node( struct node * ptr ){
if( ptr != NULL ){
ptr->left->right = ptr->right;
ptr->right->left = ptr->left;
delete ptr;
}
}

void delete_tail( ){
if( tail != NULL && tail -> left != head ){
delete_node(tail->left);
}
}

void add_to_head( struct node * ptr ){
ptr->right = head -> right;
ptr->left = head;
head -> right = ptr;
ptr -> right -> left = ptr;
}

};

Java 实现:

class LRUCache {

Cache head = null;
Cache tail = null;
int currentSize = 0;
int capacity = 0;

public LRUCache(int capacity) {
head = new Cache(0, 0);
tail = new Cache(0, 0);
head.left = tail;
head.right = tail;
tail.left = head;
tail.right = head;
this.capacity = capacity;
}

public int get(int key) {
Cache ptr = head.right;
while (ptr != tail) {
if (ptr.key == key) {
ptr.delete();
ptr.right = head.right;
ptr.left = head;
head.right = ptr;
ptr.right.left = ptr;
return ptr.value;
}
ptr = ptr.right;
}
return -1;
}

public void put(int key, int value) {
boolean isFind = false;
if (currentSize > 0) {
Cache ptr = head.right;
while (ptr != null && ptr != tail) {
if (ptr.key == key) {
ptr.delete();
// Insert
ptr.right = head.right;
ptr.left = head;
ptr.right.left = ptr;
head.right = ptr;
// Value
ptr.value = value;
isFind = true;
break;
}
ptr = ptr.right;
}
}
if (!isFind) {
Cache cache = new Cache(key, value);
if (currentSize >= capacity) {
Cache deletePtr = tail.left;
deletePtr.delete();
} else {
currentSize++;
}
Cache ptr = head.right;
head.right = cache;
cache.left = head;
cache.right = ptr;
ptr.left = cache;
}
}

private class Cache {
int key;
int value;

Cache left = null;
Cache right = null;

Cache(int key, int value) {
this.key = key;
this.value = value;
}

void delete() {
if( this.left != null ) {
this.left.right = this.right;
}
if(this.right != null ) {
this.right.left = this.left;
}
this.left = null;
this.right = null;
}
}
}