From 625832361cc8239f679c6f5744689dead901bd67 Mon Sep 17 00:00:00 2001
From: kyriewhluo <kyriewhluo@tencent.com>
Date: Thu, 15 Aug 2024 15:35:23 +0800
Subject: [PATCH] =?UTF-8?q?=E5=AE=9E=E7=8E=B0LRU=E7=BC=93=E5=AD=98?=
 =?UTF-8?q?=E6=9C=BA=E5=88=B6=E4=BB=A5=E8=A7=A3=E5=86=B3LeeCode146?=
 =?UTF-8?q?=E9=97=AE=E9=A2=98?=
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实现了一个基于哈希表和双向链表的LRU(最近最少使用)缓存机制。该机制通过在双向链表的尾部添加最近使用的元素，并从头部移除最近最少使用的元素，以维护一个固定大小的缓存。当缓存满时，通过移除头部元素来腾出空间。此实现支持get和put操作，符合LRU缓存策略的要求。
---
 .../cn/whaifree/leetCode/Hash/LeeCode146.java | 126 ++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 src/main/java/cn/whaifree/leetCode/Hash/LeeCode146.java

diff --git a/src/main/java/cn/whaifree/leetCode/Hash/LeeCode146.java b/src/main/java/cn/whaifree/leetCode/Hash/LeeCode146.java
new file mode 100644
index 0000000..8f86c21
--- /dev/null
+++ b/src/main/java/cn/whaifree/leetCode/Hash/LeeCode146.java
@@ -0,0 +1,126 @@
+package cn.whaifree.leetCode.Hash;
+
+import cn.whaifree.leetCode.model.ListNode;
+import org.junit.Test;
+
+import java.security.Key;
+import java.util.HashMap;
+
+public class LeeCode146 {
+
+    @Test
+    public void test()
+    {
+        LRUCache lruCache = new LRUCache(2);
+        lruCache.put(1, 1);
+        lruCache.put(2, 2);
+        System.out.println(lruCache.get(1));
+        lruCache.put(3, 3);
+        System.out.println(lruCache.get(2));
+        lruCache.put(4, 4);
+        System.out.println(lruCache.get(1));
+        System.out.println(lruCache.get(3));
+        System.out.println(lruCache.get(4));
+
+
+    }
+
+    class LRUCache {
+
+        static class EntryNode {
+            Integer key = null;
+            Integer object = null;
+            EntryNode pre = null;
+            EntryNode after = null;
+
+            public EntryNode(Integer object, EntryNode pre, EntryNode after) {
+                this.object = object;
+                this.pre = pre;
+                this.after = after;
+            }
+
+            public EntryNode(Integer key ,Integer object) {
+                this.key = key;
+                this.object = object;
+            }
+
+            public EntryNode() {
+            }
+        }
+
+        HashMap<Integer,EntryNode> caches;
+        EntryNode head;
+        EntryNode tail;
+        Integer size = null;
+
+
+        public LRUCache(int capacity) {
+            caches = new HashMap<>();
+            size = capacity;
+            head = new EntryNode();
+            tail = new EntryNode();
+            head.after = tail;
+            tail.pre = head;
+        }
+
+        /**
+         * 1. 先判断hashmap中有没有
+         * 2. 如果有
+         *
+         * @param key
+         * @return
+         */
+        public int get(int key) {
+            EntryNode entryNode = caches.get(key);
+            if (entryNode == null) {
+                return -1;
+            }
+            deleteNode(entryNode);
+            addNode(entryNode);
+            return entryNode.object;
+        }
+
+        public void put(int key, int value) {
+
+            if (caches.containsKey(key)) {
+                EntryNode entryNode = caches.get(key);
+                entryNode.object = value;
+                deleteNode(entryNode);
+                addNode(entryNode);
+                return;
+            }
+
+            EntryNode v = new EntryNode(key,value);
+            caches.put(key, v);
+            addNode(v);
+            if (caches.size() > size) {
+                //删除最早那个
+                caches.remove(head.after.key);
+                deleteNode(head.after);
+            }
+        }
+
+
+        /**
+         * 删除某个节点
+         * @param entryNode
+         */
+        public void deleteNode(EntryNode entryNode) {
+            entryNode.pre.after = entryNode.after;
+            entryNode.after.pre = entryNode.pre;
+        }
+
+        /**
+         * 在尾部增加某个节点
+         * @param node
+         */
+        public void addNode(EntryNode node) {
+            EntryNode pre = tail.pre;
+            pre.after = node;
+            node.pre = pre;
+            node.after = tail;
+            tail.pre = node;
+        }
+    }
+
+}