239. 滑动窗口最大值

Author: w2xi

Diff for: README.md

@@ -95,6 +95,7 @@
 |235|[二叉搜索树的最近公共祖先](https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-search-tree/)|[JavaScript](./algorithms/lowest-common-ancestor-of-a-binary-search-tree.js)|Easy|
 |236|[二叉树的最近公共祖先](https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-tree/)|[JavaScript](./algorithms/lowest-common-ancestor-of-a-binary-tree.js)|Medium|
 |237|[删除链表中的节点](https://leetcode-cn.com/problems/delete-node-in-a-linked-list/)|[JavaScript](./algorithms/delete-node-in-a-linked-list.js)|Easy|
+|239|[滑动窗口最大值](https://leetcode.cn/problems/sliding-window-maximum/)|[JavaScript](./algorithms/sliding-window-maximum.js)|Hard|
 |242|[有效的字母异位词](https://leetcode.cn/problems/valid-anagram/)|[JavaScript](./algorithms/valid-anagram.js)|Easy|
 |257|[二叉树的所有路径](https://leetcode.cn/problems/binary-tree-paths/)|[JavaScript](./algorithms/binary-tree-paths.js)|Easy|
 |283|[移动零](https://leetcode.cn/problems/move-zeroes/)|[JavaScript](./algorithms/move-zeroes.js)|Easy|

Diff for: algorithms/sliding-window-maximum.js

@@ -0,0 +1,59 @@
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var maxSlidingWindow = function (nums, k) {
+  // 单调队列
+  const deque = new Deque();
+  const result = [];
+
+  // 先将前 k 个元素放进队列
+  for (let i = 0; i < k; i++) {
+    deque.push(nums[i]);
+  }
+  // 记录前 k 个元素的最大值
+  result.push(deque.front());
+
+  for (let i = k; i < nums.length; i++) {
+    const curr = nums[i];
+    // 滑动窗口移除最前面元素
+    deque.pop(nums[i - k]);
+    // 滑动窗口前加入最后面的元素
+    deque.push(curr);
+    // 记录对应的最大值
+    result.push(deque.front());
+  }
+
+  return result;
+};
+
+/**
+ * 单调队列 (递减)
+ */
+class Deque {
+  constructor() {
+    this.queue = [];
+  }
+
+  push(val) {
+    if (this.queue.length === 0) {
+      this.queue.push(val);
+    } else {
+      while (this.queue.length > 0 && val > this.queue.at(-1)) {
+        this.queue.pop();
+      }
+      this.queue.push(val);
+    }
+  }
+
+  pop(val) {
+    if (val === this.front()) {
+      this.queue.shift();
+    }
+  }
+
+  front() {
+    return this.queue[0];
+  }
+}