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修复了map无法删除元素的问题 #4

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Merged
hicf merged 1 commit into from
Sep 1, 2019
Merged

修复了map无法删除元素的问题 #4

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51 changes: 28 additions & 23 deletions resource/markdown/algorithm/LRUCache.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ public class LRUCache<K, V> {
/**
* 默认容量
*/
private int DEFAULT_CAPACITY = 1024;
private static final int DEFAULT_CAPACITY = 1024;
/**
* 缓存容量
*/
Expand All @@ -19,19 +19,21 @@ public class LRUCache<K, V> {
/**
* 高效访问的散列表
*/
private Map<K, Node<V>> map;
private Map<K, Node<K, V>> map;

private Node<V> head, tail;
private Node<K, V> head, tail;

/**
* 自定义双向链表中的节点
*/
private static class Node<V> {
private static class Node<K, V> {
K key;
V value;
Node<V> prev;
Node<V> next;
Node<K, V> prev;
Node<K, V> next;

Node(Node<V> prev, V value, Node<V> next) {
Node(Node<K, V> prev, K key, V value, Node<K, V> next) {
this.key = key;
this.value = value;
this.prev = prev;
this.next = next;
Expand All @@ -46,14 +48,18 @@ public class LRUCache<K, V> {
}

public LRUCache(int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException("Capacity must be positive integer");
}

this.capacity = capacity;
this.map = new HashMap<>(capacity, 0.75F);
this.head = null;
this.tail = null;
}

public V get(K key) {
Node<V> node = this.map.get(key);
Node<K, V> node = this.map.get(key);
if (node != null) {
this.moveToHead(node);
return node.value;
Expand All @@ -63,19 +69,19 @@ public class LRUCache<K, V> {
}

public V put(K key, V value) {
Node<V> node = this.map.get(key);
Node<K, V> node = this.map.get(key);
if (node != null) {
node.value = value;
moveToHead(node);
return value;
}

if (size == capacity) {
removeLast();
map.remove(key);
node = removeLast();
map.remove(node.key);
}

node = addFirst(value);
node = addFirst(key, value);
map.put(key, node);

return value;
Expand All @@ -84,9 +90,9 @@ public class LRUCache<K, V> {
/**
* 对于新添加的元素，应将新元素添加到链表的头部
*/
private Node<V> addFirst(V e) {
final Node<V> h = head;
final Node<V> newNode = new Node<>(null, e, h);
private Node<K, V> addFirst(K key, V value) {
final Node<K, V> h = head;
final Node<K, V> newNode = new Node<>(null, key, value, h);
head = newNode;
if (h == null) {
tail = newNode;
Expand All @@ -101,9 +107,9 @@ public class LRUCache<K, V> {
/**
* 对于被访问的元素，将该元素移动到头部
*/
private Node moveToHead(Node<V> node) {
final Node<V> prev = node.prev;
final Node<V> next = node.next;
private Node<K, V> moveToHead(Node<K, V> node) {
final Node<K, V> prev = node.prev;
final Node<K, V> next = node.next;

if (prev == null) { // 如果是首节点，无需移动
return node;
Expand All @@ -127,15 +133,14 @@ public class LRUCache<K, V> {
/**
* 缓存满时，应删除（淘汰）最后一个节点
*/
private V removeLast() {
final Node<V> t = tail;
private Node<K, V> removeLast() {
final Node<K, V> t = tail;
if (t == null) {
return null;
}

V element = t.value;
t.value = null; // help GC
Node<V> prev = t.prev;
Node<K, V> prev = t.prev;
t.prev = null; // help GC
tail = prev; // 移动 tail
if (prev == null) { // 如果尾节点的前一个节点也为空，说明尾节点也是首节点
Expand All @@ -144,7 +149,7 @@ public class LRUCache<K, V> {
prev.next = null;
}
size--;
return element;
return t;
}
}
```
Expand Down