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LRUCache146.java
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LRUCache146.java
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package Leetcode;
import java.util.HashMap;
import java.util.Map;
public class LRUCache146 {
/* Method : HashMap + DLinkedNode, Time: O(1), Space:O(capacity)**/
class DLinkedNode { //双向链表的定义
int key;
int value;
DLinkedNode prev;
DLinkedNode next;
public DLinkedNode() {}
public DLinkedNode(int key, int value) {
this.key = key;
this.value = value;
}
}
private Map<Integer, DLinkedNode> map = new HashMap<>();
private int size;
private int capacity;
private DLinkedNode head;
private DLinkedNode tail;
public LRUCache146(int capacity) {
this.capacity = capacity;
this.size = 0;
this.head = new DLinkedNode();
this.tail = new DLinkedNode();
head.next = tail;
tail.prev = head;
}
public int get(int key) { //每次get结束要move到头节点后面
DLinkedNode node = map.get(key);
if(node == null) {
return -1;
}
moveToHead(node);
return node.value;
}
public void put(int key, int value) {
DLinkedNode node = map.get(key);
if(node != null) { // 1.如果有,直接update, moveToHead
node.value = value;
moveToHead(node);
} else {
node = new DLinkedNode(key, value); // 2.如果没有,put, addToHead
map.put(key, node);
addToHead(node);
size ++;
if(size > capacity) { // 3.是否需要remove tail前一位
DLinkedNode tailN = removeTail();
map.remove(tailN.key);
--size;
}
}
}
private void addToHead(DLinkedNode node) {
node.prev = head;
node.next = head.next;
head.next.prev = node;
head.next = node;
}
private void removeNode(DLinkedNode node) {
node.prev.next = node.next;
node.next.prev = node.prev;
}
private DLinkedNode removeTail() {
DLinkedNode tailN = tail.prev;
removeNode(tailN);
return tailN;
}
private void moveToHead(DLinkedNode node) {
removeNode(node);
addToHead(node);
}
}