LRU 算法 Java 实现
算法 Java 面试 About 3,851 words定义
Least Recently Used
最近最少使用,是一种常用的页面置换算法。
选择最近最久未使用的数据予以淘汰。
LinkedHashMap
public class LRU_LinkedHashMap {
public static void main(String[] args) {
int capacity = 3;
LinkedHashMap<Object, Object> map = new LinkedHashMap<Object, Object>(capacity, 0.75f, true) {
@Override
protected boolean removeEldestEntry(Map.Entry eldest) {
return super.size() > capacity;
}
};
map.put(1, "a");
map.put(2, "b");
map.put(3, "c");
System.out.println(map.keySet());
map.put(4, "d");
System.out.println(map.keySet());
map.get(2);
System.out.println(map.keySet());
map.put(5, "e");
System.out.println(map.keySet());
}
}
输出:
[1, 2, 3]
[2, 3, 4]
[3, 4, 2]
[4, 2, 5]
自定义数据结构
主要思路:
- 定义
Map
和双向链表 put
/get
时,先从双向链表中删除该元素,再添加到链表头部
public class LRU_Demo {
public static void main(String[] args) {
LRU_Demo demo = new LRU_Demo(3);
demo.put(1, 1);
demo.put(2, 3);
demo.put(3, 3);
System.out.println(demo.map.keySet());
demo.put(4, 4);
System.out.println(demo.map.keySet());
demo.get(2);
System.out.println(demo.map.keySet());
demo.put(5, 5);
System.out.println(demo.map.keySet());
}
int capacity;
Map<Integer, Node<Integer, Integer>> map;
DoubleLinkedList<Integer, Integer> doubleLinkedList;
public LRU_Demo(int capacity) {
this.capacity = capacity;
map = new HashMap<>();
doubleLinkedList = new DoubleLinkedList<>();
}
public int get(int key) {
if (!map.containsKey(key)) {
return -1;
}
Node<Integer, Integer> node = map.get(key);
doubleLinkedList.removeNode(node);
doubleLinkedList.addHead(node);
return node.value;
}
public void put(int key, int value) {
if (map.containsKey(key)) {
// update
Node<Integer, Integer> node = map.get(key);
node.value = value;
doubleLinkedList.removeNode(node);
doubleLinkedList.addHead(node);
} else {
if (map.size() == capacity) {
// 容量满了,删除最后一个元素
Node<Integer, Integer> lastNode = doubleLinkedList.getLast();
map.remove(lastNode.key);
doubleLinkedList.removeNode(lastNode);
}
//
Node<Integer, Integer> node = new Node<>(key, value);
map.put(key, node);
doubleLinkedList.addHead(node);
}
}
static class Node<K, V> {
public K key;
public V value;
public Node<K, V> prev;
public Node<K, V> next;
public Node() {
}
public Node(K key, V value) {
this.key = key;
this.value = value;
}
}
static class DoubleLinkedList<K, V> {
public Node<K, V> head;
public Node<K, V> tail;
public DoubleLinkedList() {
head = new Node<>();
tail = new Node<>();
head.next = tail;
tail.prev = head;
}
public void addHead(Node<K, V> node) {
node.next = head.next;
node.prev = head;
head.next.prev = node;
head.next = node;
}
public void removeNode(Node<K, V> node) {
node.next.prev = node.prev;
node.prev.next = node.next;
node.next = null;
node.prev = null;
}
public Node<K, V> getLast() {
return tail.prev;
}
}
}
输出:
[1, 2, 3]
[2, 3, 4]
[2, 3, 4]
[2, 4, 5]
Views: 1,633 · Posted: 2022-04-17
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