[146 LRU缓存](https://leetcode.cn/problems/lru-cache/)
class LRUCache {
private int size;
private int capacity;
private Map<Integer, Node> cache = new HashMap<>();
private Node head;
private Node tail;
public LRUCache(int capacity) {
this.capacity = capacity;
this.size = 0;
this.head = new Node();
this.tail = new Node();
this.head.next = this.tail;
this.tail.prev = this.head;
}
public int get(int key) {
Node node = cache.get(key);
if (node == null) {
return -1;
}
moveToHead(node);
return node.value;
}
public void put(int key, int value) {
Node node = cache.get(key);
if (node == null) {
node = new Node(key, value);
cache.put(key, node);
addToHead(node);
size++;
if (size > capacity) {
Node tail = removeTail();
cache.remove(tail.key);
size--;
}
}
node.value = value;
moveToHead(node);
}
private void addToHead(Node node) {
node.prev = head;
node.next = head.next;
head.next.prev = node;
head.next = node;
}
private void removeNode(Node node) {
node.prev.next = node.next;
node.next.prev = node.prev;
}
private void moveToHead(Node node) {
removeNode(node);
addToHead(node);
}
private Node removeTail() {
Node res = tail.prev;
removeNode(res);
return res;
}
class Node {
int key;
int value;
Node prev;
Node next;
public Node(int key, int value) {
this.key = key;
this.value = value;
}
public Node() {
}
}
}