警告
本文最后更新于 2022-09-09，文中内容可能已过时。
LRU (Least Recently Used)
最近最少使用算法。当容量满时，将最久没有使用过的缓存删除。
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| class Node {
int key, val;
Node prev, next;
public Node(int key, int val) {
this.key = key;
this.val = val;
}
}
class BiLinkedList {
final Node head, tail;
final int capacity;
int length;
public BiLinkedList(int capacity) {
this.capacity = capacity;
length = 0;
head = new Node(0, 0);
tail = new Node(0, 0);
head.next = tail;
tail.prev = head;
}
/**
* 将结点加入双向链表的尾部
*
* @param node 待加入结点
*/
public void addLast(Node node) {
node.prev = tail.prev;
node.next = tail;
node.prev.next = node;
tail.prev = node;
length++;
}
/**
* 将 node 从双向链表中删除
*
* @param node 待加入结点
*/
public void remove(Node node) {
node.prev.next = node.next;
node.next.prev = node.prev;
length--;
}
/**
* 将双向链表的第一个结点删除
*/
public void removeFirst() {
if (length == 0) {
return;
}
head.next = head.next.next;
head.next.prev = head;
length--;
}
}
class LRUCache {
private BiLinkedList list;
private HashMap<Integer, Node> keyToNode;
public LRUCache(int capacity) {
list = new BiLinkedList(capacity);
keyToNode = new HashMap<>();
}
public int get(int key) {
if (keyToNode.containsKey(key)) {
Node node = keyToNode.get(key);
list.remove(node);
list.addLast(node);
return node.val;
} else {
return -1;
}
}
public void put(int key, int value) {
if (keyToNode.containsKey(key)) {
Node node = keyToNode.get(key);
node.val = value;
list.remove(node);
list.addLast(node);
} else {
if (list.length == list.capacity) {
keyToNode.remove(list.head.next.key);
list.removeFirst();
}
Node node = new Node(key, value);
keyToNode.put(key, node);
list.addLast(node);
}
}
}
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| class LRUCache {
class ListNode {
int key, val;
ListNode prev, next;
public ListNode(int key, int val) {
this.key = key;
this.val = val;
}
}
HashMap<Integer, ListNode> key2node;
ListNode head; // 双链表头结点
int capacity;
public LRUCache(int capacity) {
key2node = new HashMap<>();
head = new ListNode(0, 0);
head.prev = head.next = head; // 循环链表
this.capacity = capacity;
}
public int get(int key) {
ListNode node = key2node.get(key);
if (node == null) return -1;
// 取出 node
node.prev.next = node.next;
node.next.prev = node.prev;
// node 插入末尾
head.prev.next = node;
node.prev = head.prev;
node.next = head;
head.prev = node;
return node.val;
}
public void put(int key, int value) {
ListNode node = key2node.get(key);
if (node != null) {
// 取出 node
node.prev.next = node.next;
node.next.prev = node.prev;
node.val = value;
} else {
node = new ListNode(key, value);
key2node.put(key, node);
}
// node 插入末尾
head.prev.next = node;
node.prev = head.prev;
node.next = head;
head.prev = node;
if (key2node.size() > capacity) {
// 删除第一个结点
key2node.remove(head.next.key);
head.next = head.next.next;
head.next.prev = head;
}
}
}
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| class LRUCache {
private LinkedHashMap<Integer, Integer> data;
private int capacity;
public LRUCache(int capacity) {
this.data = new LinkedHashMap<>();
this.capacity = capacity;
}
public int get(int key) {
int val = data.getOrDefault(key, -1);
if (data.containsKey(key)) {
data.remove(key);
data.put(key, val);
}
return val;
}
public void put(int key, int value) {
data.remove(key);
data.put(key, value);
if (data.size() > this.capacity) {
data.remove(data.keySet().iterator().next());
}
}
}
|