<h2 id="lru">LRU缓存机制</h2>
<p>运用你所掌握的数据结构，设计和实现一个 LRU (最近最少使用) 缓存机制。它应该支持以下操作： 获取数据 get 和 写入数据 put 。<br></p>
<p>获取数据 get(key) - 如果密钥 (key) 存在于缓存中，则获取密钥的值（总是正数），否则返回 -1。<br></p>
<p>写入数据 put(key, value) - 如果密钥已经存在，则变更其数据值；如果密钥不存在，则插入该组「密钥/数据值」。当缓存容量达到上限时，它应该在写入新数据之前删除最久未使用的数据值，从而为新的数据值留出空间。</p>
<p><strong>示例:</strong></p>
<pre><code>LRUCache cache = new LRUCache( 2 /* 缓存容量 */ );

cache.put(1, 1);
cache.put(2, 2);
cache.get(1);       // 返回  1
cache.put(3, 3);    // 该操作会使得密钥 2 作废
cache.get(2);       // 返回 -1 (未找到)
cache.put(4, 4);    // 该操作会使得密钥 1 作废
cache.get(1);       // 返回 -1 (未找到)
cache.get(3);       // 返回  3
cache.get(4);       // 返回  4
</code></pre>
<h3 id="">思路</h3>
<p>维护待删除 key 值的队列，根据使用情况对 key 值进行位置调整。</p>
<pre><code>/**
 * @param {number} capacity
 */
var LRUCache = function (capacity) {
  this.capacity = capacity;
  this.usedCapacity = 0;
  this.store = Object.create(null);
  this.toDeleteKeys = [];
};

/**
 * @param {number} key
 * @return {number}
 */
LRUCache.prototype.get = function (key) {
  if (this.store[key]) {
    this.moveKeyToEnd(key);
  }

  return this.store[key] || -1;
};

LRUCache.prototype.moveKeyToEnd = function (key) {
  let arr = this.toDeleteKeys;
  let idx = this.toDeleteKeys.indexOf(key);

  if (idx &lt; 0) {
    return;
  }

  if (idx === arr.length - 1) {
    return;
  }

  arr.splice(idx, 1);
  arr.push(key);
};

/**
 * @param {number} key
 * @param {number} value
 * @return {void}
 */
LRUCache.prototype.put = function (key, value) {
  if (this.store[key]) {
    this.moveKeyToEnd(key);
    this.store[key] = value;
    return;
  }

  this.toDeleteKeys.push(key);

  if (this.usedCapacity &lt; this.capacity) {
    this.store[key] = value;
    this.usedCapacity += 1;
  } else {
    let deleteKey = this.toDeleteKeys.shift();
    delete this.store[deleteKey];
    this.store[key] = value;
  }
};
</code></pre>
<p>运行结果：</p>
<pre><code>Accepted
18/18 cases passed (256 ms)
Your runtime beats 38.35 % of javascript submissions
Your memory usage beats 100 % of javascript submissions (58.9 MB)
</code></pre>

LeetCode：LRU缓存机制

# Leetcode

✅ Solutions to LeetCode by JavaScript.

## 简单

- [两数之和](https://github.com/fantasticit/LeetCode/tree/master/Easy/0001.两数之和.js)
- [整数反转](https://github.com/fantasticit/LeetCode/tree/master/Easy/0007.整数反转.js)
- [回文数](https://github.com/fantasticit/LeetCode/tree/master/Easy/0009.回文数.js)
- [有效的括号](https://github.com/fantasticit/LeetCode/tree/master/Easy/0020.有效的括号.js)
- [合并两个有序链表](https://github.com/fantasticit/LeetCode/tree/master/Easy/0021.合并两个有序链表.js)
- [删除排序数组中的重复项](https://github.com/fantasticit/LeetCode/tree/master/Easy/0026.删除排序数组中的重复项.js)
- [移除元素](https://github.com/fantasticit/LeetCode/tree/master/Easy/0027.移除元素.js)
- [实现-str-str](https://github.com/fantasticit/LeetCode/tree/master/Easy/0028.实现-str-str.js)
- [搜索插入位置](https://github.com/fantasticit/LeetCode/tree/master/Easy/0035.搜索插入位置.js)
- [最大子序和](https://github.com/fantasticit/LeetCode/tree/master/Easy/0053.最大子序和.js)
- [最后一个单词的长度](https://github.com/fantasticit/LeetCode/tree/master/Easy/0058.最后一个单词的长度.js)
- [加一](https://github.com/fantasticit/LeetCode/tree/master/Easy/0066.加一.js)
- [二进制求和](https://github.com/fantasticit/LeetCode/tree/master/Easy/0067.二进制求和.js)
- [爬楼梯](https://github.com/fantasticit/LeetCode/tree/master/Easy/0070.爬楼梯.js)
- [删除排序链表中的重复元素](https://github.com/fantasticit/LeetCode/tree/master/Easy/0083.删除排序链表中的重复元素.js)
- [合并两个有序数组](https://github.com/fantasticit/LeetCode/tree/master/Easy/0088.合并两个有序数组.js)
- [相同的树](https://github.com/fantasticit/LeetCode/tree/master/Easy/0100.相同的树.js)
- [对称二叉树](https://github.com/fantasticit/LeetCode/tree/master/Easy/0101.对称二叉树.js)
- [二叉树的最大深度](https://github.com/fantasticit/LeetCode/tree/master/Easy/0104.二叉树的最大深度.js)
- [二叉树的层次遍历-ii](https://github.com/fantasticit/LeetCode/tree/master/Easy/0107.二叉树的层次遍历-ii.js)
- [平衡二叉树](https://github.com/fantasticit/LeetCode/tree/master/Easy/0110.平衡二叉树.js)
- [二叉树的最小深度](https://github.com/fantasticit/LeetCode/tree/master/Easy/0111.二叉树的最小深度.js)
- [只出现一次的数字](https://github.com/fantasticit/LeetCode/tree/master/Easy/0136.只出现一次的数字.js)
- [环形链表](https://github.com/fantasticit/LeetCode/tree/master/Easy/0141.环形链表.js)
- [反转链表](https://github.com/fantasticit/LeetCode/tree/master/Easy/0206.反转链表.js)
- [最小栈](https://github.com/fantasticit/LeetCode/tree/master/Easy/0155.最小栈.js)
- [移除链表元素](https://github.com/fantasticit/LeetCode/tree/master/Easy/0203.移除链表元素.js)
- [存在重复元素](https://github.com/fantasticit/LeetCode/tree/master/Easy/0217.存在重复元素.js)
- [回文链表](https://github.com/fantasticit/LeetCode/tree/master/Easy/0234.回文链表.js)
- [各位相加](https://github.com/fantasticit/LeetCode/tree/master/Easy/0258.各位相加.js)
- [反转字符串](https://github.com/fantasticit/LeetCode/tree/master/Easy/0344.反转字符串.js)
- [找不同](https://github.com/fantasticit/LeetCode/tree/master/Easy/0389.找不同.js)
- [用队列实现栈](https://github.com/fantasticit/LeetCode/tree/master/Easy/0225.用队列实现栈.js)
- [斐波那契数](https://github.com/fantasticit/LeetCode/tree/master/Easy/0509.斐波那契数.js)
- [二分查找](https://github.com/fantasticit/LeetCode/tree/master/Easy/0704.二分查找)
- [反转字符串-ii](https://github.com/fantasticit/LeetCode/tree/master/Easy/0541.反转字符串-ii.js)

## 中等

- [两数相加](https://github.com/fantasticit/LeetCode/tree/master/Medium/0002.两数相加.js)
- [字符串转换整数-atoi](https://github.com/fantasticit/LeetCode/tree/master/Medium/0008.字符串转换整数-atoi.js)
- [盛最多水的容器](https://github.com/fantasticit/LeetCode/tree/master/Medium/0011.盛最多水的容器.js)
- [三数之和](https://github.com/fantasticit/LeetCode/tree/master/Medium/0015.三数之和.js)
- [最接近的三数之和](https://github.com/fantasticit/LeetCode/tree/master/Medium/0016.最接近的三数之和.js)
- [四数之和](https://github.com/fantasticit/LeetCode/tree/master/Medium/0018.四数之和.js)
- [删除链表的倒数第 n 个节点](https://github.com/fantasticit/LeetCode/tree/master/Medium/0019.删除链表的倒数第n个节点.js)
- [括号生成](https://github.com/fantasticit/LeetCode/tree/master/Medium/0022.括号生成.js)
- [两两交换链表中的节点](https://github.com/fantasticit/LeetCode/tree/master/Medium/0024.两两交换链表中的节点.js)
- [两数相除](https://github.com/fantasticit/LeetCode/tree/master/Medium/0029.两数相除.js)
- [在排序数组中查找元素的第一个和最后一个位置](https://github.com/fantasticit/LeetCode/tree/master/Medium/0034.在排序数组中查找元素的第一个和最后一个位置.js)
- [有效的数独](https://github.com/fantasticit/LeetCode/tree/master/Medium/0036.有效的数独.js)
- [字符串相乘](https://github.com/fantasticit/LeetCode/tree/master/Medium/0043.字符串相乘.js)
- [字母异位词分组](https://github.com/fantasticit/LeetCode/tree/master/Medium/0049.字母异位词分组.js)
- [pow-x-n](https://github.com/fantasticit/LeetCode/tree/master/Medium/0050.pow-x-n.js)
- [二叉树的前序遍历](https://github.com/fantasticit/LeetCode/tree/master/Medium/0144.二叉树的前序遍历.js)
- [lru 缓存机制](https://github.com/fantasticit/LeetCode/tree/master/Medium/0146.lru缓存机制.js)
- [最长上升子序列](https://github.com/fantasticit/LeetCode/tree/master/Medium/0300.最长上升子序列)
- [二叉树的中序遍历](https://github.com/fantasticit/LeetCode/tree/master/Medium/0094.二叉树的中序遍历)

## 困难

- [缺失的第一个正数](https://github.com/fantasticit/LeetCode/tree/master/Hard/0041.缺失的第一个正数.js)
- [最小覆盖子串](https://github.com/fantasticit/LeetCode/tree/master/Hard/0076.最小覆盖子串)
- [二叉树的后序遍历](https://github.com/fantasticit/LeetCode/tree/master/Hard/0145.二叉树的后序遍历)

## LICENSE

MIT
