A: new

Author: Shuo

README.md

@@ -11,54 +11,45 @@
 
 ## [954. Array of Doubled Pairs (Medium)](https://leetcode.com/problems/array-of-doubled-pairs "二倍数对数组")
 
-<p>Given an array of integers <code>A</code>&nbsp;with even length, return <code>true</code> if and only if it is possible to reorder it such that <code>A[2 * i + 1] = 2 * A[2 * i]</code> for every <code>0 &lt;=&nbsp;i &lt; len(A) / 2</code>.</p>
-
-<div>
-<div>
-<div>
-<ol>
-</ol>
-</div>
-</div>
-</div>
+<p>Given an array of integers <code>arr</code> of even length, return <code>true</code> if and only if it is possible to reorder it such that <code>arr[2 * i + 1] = 2 * arr[2 * i]</code> for every <code>0 &lt;= i &lt; len(arr) / 2</code>.</p>
 
 <p>&nbsp;</p>
 <p><strong>Example 1:</strong></p>
 
 <pre>
-<strong>Input:</strong> A = [3,1,3,6]
+<strong>Input:</strong> arr = [3,1,3,6]
 <strong>Output:</strong> false
 </pre>
 
 <p><strong>Example 2:</strong></p>
 
 <pre>
-<strong>Input:</strong> A = [2,1,2,6]
+<strong>Input:</strong> arr = [2,1,2,6]
 <strong>Output:</strong> false
 </pre>
 
 <p><strong>Example 3:</strong></p>
 
 <pre>
-<strong>Input:</strong> A = [4,-2,2,-4]
+<strong>Input:</strong> arr = [4,-2,2,-4]
 <strong>Output:</strong> true
 <strong>Explanation:</strong> We can take two groups, [-2,-4] and [2,4] to form [-2,-4,2,4] or [2,4,-2,-4].
 </pre>
 
 <p><strong>Example 4:</strong></p>
 
 <pre>
-<strong>Input:</strong> A = [1,2,4,16,8,4]
+<strong>Input:</strong> arr = [1,2,4,16,8,4]
 <strong>Output:</strong> false
 </pre>
 
 <p>&nbsp;</p>
 <p><strong>Constraints:</strong></p>
 
 <ul>
-	<li><code>0 &lt;= A.length &lt;= 3 *&nbsp;10<sup>4</sup></code></li>
-	<li><code>A.length</code> is even.</li>
-	<li><code>-10<sup>5</sup> &lt;= A[i] &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= arr.length &lt;= 3 * 10<sup>4</sup></code></li>
+	<li><code>arr.length</code> is even.</li>
+	<li><code>-10<sup>5</sup> &lt;= arr[i] &lt;= 10<sup>5</sup></code></li>
 </ul>
 
 ### Related Topics

problems/array-of-doubled-pairs/README.md

@@ -23,7 +23,7 @@
 <pre>
 <strong>Input:</strong> asteroids = [5,10,-5]
 <strong>Output:</strong> [5,10]
-<b>Explanation:</b> The 10 and -5 collide resulting in 10.  The 5 and 10 never collide.
+<b>Explanation:</b> The 10 and -5 collide resulting in 10. The 5 and 10 never collide.
 </pre>
 
 <p><strong>Example 2:</strong></p>
@@ -54,7 +54,7 @@
 <p><strong>Constraints:</strong></p>
 
 <ul>
-	<li><code>1 &lt;= asteroids &lt;= 10<sup>4</sup></code></li>
+	<li><code>2 &lt;= asteroids &lt;= 10<sup>4</sup></code></li>
 	<li><code>-1000 &lt;= asteroids[i] &lt;= 1000</code></li>
 	<li><code>asteroids[i] != 0</code></li>
 </ul>

problems/asteroid-collision/README.md

@@ -9,6 +9,6 @@
 
 [Next >](../check-if-two-string-arrays-are-equivalent "Check If Two String Arrays are Equivalent")
 
-## [1661. Average Time of Process per Machine (Easy)](https://leetcode.com/problems/average-time-of-process-per-machine "")
+## [1661. Average Time of Process per Machine (Easy)](https://leetcode.com/problems/average-time-of-process-per-machine "每台机器的进程平均运行时间")
 
 

problems/average-time-of-process-per-machine/README.md

@@ -11,29 +11,38 @@
 
 ## [121. Best Time to Buy and Sell Stock (Easy)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock "买卖股票的最佳时机")
 
-<p>Say you have an array for which the <em>i</em><sup>th</sup> element is the price of a given stock on day <em>i</em>.</p>
+<p>You are given an array <code>prices</code> where <code>prices[i]</code> is the price of a given stock on the <code>i<sup>th</sup></code> day.</p>
 
-<p>If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.</p>
+<p>You want to maximize your profit by choosing a <strong>single day</strong> to buy one stock and choosing a <strong>different day in the future</strong> to sell that stock.</p>
 
-<p>Note that you cannot sell a stock before you buy one.</p>
+<p>Return <em>the maximum profit you can achieve from this transaction</em>. If you cannot achieve any profit, return <code>0</code>.</p>
 
+<p>&nbsp;</p>
 <p><strong>Example 1:</strong></p>
 
 <pre>
-<strong>Input:</strong> [7,1,5,3,6,4]
+<strong>Input:</strong> prices = [7,1,5,3,6,4]
 <strong>Output:</strong> 5
 <strong>Explanation:</strong> Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
-&nbsp;            Not 7-1 = 6, as selling price needs to be larger than buying price.
+Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
 </pre>
 
 <p><strong>Example 2:</strong></p>
 
 <pre>
-<strong>Input:</strong> [7,6,4,3,1]
+<strong>Input:</strong> prices = [7,6,4,3,1]
 <strong>Output:</strong> 0
-<strong>Explanation:</strong> In this case, no transaction is done, i.e. max profit = 0.
+<strong>Explanation:</strong> In this case, no transactions are done and the max profit = 0.
 </pre>
 
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= prices.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= prices[i] &lt;= 10<sup>4</sup></code></li>
+</ul>
+
 ### Related Topics
   [[Array](../../tag/array/README.md)]
   [[Dynamic Programming](../../tag/dynamic-programming/README.md)]

problems/best-time-to-buy-and-sell-stock/README.md

@@ -11,23 +11,27 @@
 
 ## [124. Binary Tree Maximum Path Sum (Hard)](https://leetcode.com/problems/binary-tree-maximum-path-sum "二叉树中的最大路径和")
 
-<p>Given the <code>root</code> of a binary tree, return <em>the maximum path sum</em>.</p>
+<p>A <strong>path</strong> in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence <strong>at most once</strong>. Note that the path does not need to pass through the root.</p>
 
-<p>For this problem, a path is defined as any node sequence from some starting node to any node in the tree along the parent-child connections. The path must contain <strong>at least one node</strong> and does not need to go through the root.</p>
+<p>The <strong>path sum</strong> of a path is the sum of the node&#39;s values in the path.</p>
+
+<p>Given the <code>root</code> of a binary tree, return <em>the maximum <strong>path sum</strong> of any path</em>.</p>
 
 <p>&nbsp;</p>
 <p><strong>Example 1:</strong></p>
 <img alt="" src="https://assets.leetcode.com/uploads/2020/10/13/exx1.jpg" style="width: 322px; height: 182px;" />
 <pre>
 <strong>Input:</strong> root = [1,2,3]
 <strong>Output:</strong> 6
+<strong>Explanation:</strong> The optimal path is 2 -&gt; 1 -&gt; 3 with a path sum of 2 + 1 + 3 = 6.
 </pre>
 
 <p><strong>Example 2:</strong></p>
 <img alt="" src="https://assets.leetcode.com/uploads/2020/10/13/exx2.jpg" />
 <pre>
 <strong>Input:</strong> root = [-10,9,20,null,null,15,7]
 <strong>Output:</strong> 42
+<strong>Explanation:</strong> The optimal path is 15 -&gt; 20 -&gt; 7 with a path sum of 15 + 20 + 7 = 42.
 </pre>
 
 <p>&nbsp;</p>

problems/binary-tree-maximum-path-sum/README.md

@@ -58,12 +58,7 @@
 </ul>
 
 <p>&nbsp;</p>
-
-<p><strong>Follow up:</strong></p>
-
-<p>Recursive solution is trivial, could you do it iteratively?</p>
-
-<p>&nbsp;</p>
+<p><strong>Follow up:</strong> Recursive solution is trivial, could you do it iteratively?</p>
 
 ### Related Topics
   [[Stack](../../tag/stack/README.md)]

problems/binary-tree-preorder-traversal/README.md

@@ -11,49 +11,42 @@
 
 ## [881. Boats to Save People (Medium)](https://leetcode.com/problems/boats-to-save-people "救生艇")
 
-<p>The <code>i</code>-th person has weight <code>people[i]</code>, and each boat can carry a maximum weight of <code>limit</code>.</p>
+<p>You are given an array <code>people</code> where <code>people[i]</code> is the weight of the <code>i<sup>th</sup></code> person, and an <strong>infinite number of boats</strong> where each boat can carry a maximum weight of <code>limit</code>. Each boat carries at most two people at the same time, provided the sum of the weight of those people is at most <code>limit</code>.</p>
 
-<p>Each boat carries at most 2 people at the same time, provided the sum of the&nbsp;weight of those people is at most <code>limit</code>.</p>
-
-<p>Return the minimum number of boats to carry every given person.&nbsp; (It is guaranteed each person can be carried by a boat.)</p>
+<p>Return <em>the minimum number of boats to carry every given person</em>.</p>
 
 <p>&nbsp;</p>
-
-<div>
 <p><strong>Example 1:</strong></p>
 
 <pre>
-<strong>Input: </strong>people = <span id="example-input-1-1">[1,2]</span>, limit = <span id="example-input-1-2">3</span>
-<strong>Output: </strong><span id="example-output-1">1</span>
-<strong>Explanation: </strong>1 boat (1, 2)
+<strong>Input:</strong> people = [1,2], limit = 3
+<strong>Output:</strong> 1
+<strong>Explanation:</strong> 1 boat (1, 2)
 </pre>
 
-<div>
 <p><strong>Example 2:</strong></p>
 
 <pre>
-<strong>Input: </strong>people = <span id="example-input-2-1">[3,2,2,1]</span>, limit = <span id="example-input-2-2">3</span>
-<strong>Output: </strong><span id="example-output-2">3</span>
-<strong>Explanation</strong>: 3 boats (1, 2), (2) and (3)
+<strong>Input:</strong> people = [3,2,2,1], limit = 3
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> 3 boats (1, 2), (2) and (3)
 </pre>
 
-<div>
 <p><strong>Example 3:</strong></p>
 
 <pre>
-<strong>Input: </strong>people = <span id="example-input-3-1">[3,5,3,4]</span>, limit = <span id="example-input-3-2">5</span>
-<strong>Output: </strong><span id="example-output-3">4</span>
-<strong>Explanation</strong>: 4 boats (3), (3), (4), (5)</pre>
+<strong>Input:</strong> people = [3,5,3,4], limit = 5
+<strong>Output:</strong> 4
+<strong>Explanation:</strong> 4 boats (3), (3), (4), (5)
+</pre>
 
-<p><strong>Note</strong>:</p>
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
 
 <ul>
-	<li><code>1 &lt;=&nbsp;people.length &lt;= 50000</code></li>
-	<li><code>1 &lt;= people[i] &lt;=&nbsp;limit &lt;= 30000</code></li>
+	<li><code>1 &lt;= people.length &lt;= 5 * 10<sup>4</sup></code></li>
+	<li><code>1 &lt;= people[i] &lt;= limit &lt;= 3 * 10<sup>4</sup></code></li>
 </ul>
-</div>
-</div>
-</div>
 
 ### Related Topics
   [[Greedy](../../tag/greedy/README.md)]

problems/boats-to-save-people/README.md

@@ -0,0 +1,76 @@
+<!--|This file generated by command(leetcode description); DO NOT EDIT.    |-->
+<!--+----------------------------------------------------------------------+-->
+<!--|@author    openset <[email protected]>                           |-->
+<!--|@link      https://github.com/openset                                 |-->
+<!--|@home      https://github.com/openset/leetcode                        |-->
+<!--+----------------------------------------------------------------------+-->
+
+[< Previous](../find-kth-largest-xor-coordinate-value "Find Kth Largest XOR Coordinate Value")
+　　　　　　　　　　　　　　　　
+[Next >](../find-distance-in-a-binary-tree "Find Distance in a Binary Tree")
+
+## [1739. Building Boxes (Hard)](https://leetcode.com/problems/building-boxes "放置盒子")
+
+<p>You have a cubic storeroom where the width, length, and height of the room are all equal to <code>n</code> units. You are asked to place <code>n</code> boxes in this room where each box is a cube of unit side length. There are however some rules to placing the boxes:</p>
+
+<ul>
+	<li>You can place the boxes anywhere on the floor.</li>
+	<li>If box <code>x</code> is placed on top of the box <code>y</code>, then each side of the four vertical sides of the box <code>y</code> <strong>must</strong> either be adjacent to another box or to a wall.</li>
+</ul>
+
+<p>Given an integer <code>n</code>, return<em> the <strong>minimum</strong> possible number of boxes touching the floor.</em></p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<p><img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/3-boxes.png" style="width: 135px; height: 143px;" /></p>
+
+<pre>
+<strong>Input:</strong> n = 3
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The figure above is for the placement of the three boxes.
+These boxes are placed in the corner of the room, where the corner is on the left side.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<p><img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/4-boxes.png" style="width: 135px; height: 179px;" /></p>
+
+<pre>
+<strong>Input:</strong> n = 4
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The figure above is for the placement of the four boxes.
+These boxes are placed in the corner of the room, where the corner is on the left side.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<p><img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/10-boxes.png" style="width: 271px; height: 257px;" /></p>
+
+<pre>
+<strong>Input:</strong> n = 10
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> The figure above is for the placement of the ten boxes.
+These boxes are placed in the corner of the room, where the corner is on the back side.</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= n &lt;= 10<sup>9</sup></code></li>
+</ul>
+
+### Related Topics
+  [[Math](../../tag/math/README.md)]
+  [[Binary Search](../../tag/binary-search/README.md)]
+
+### Hints
+<details>
+<summary>Hint 1</summary>
+Suppose We can put m boxes on the floor, within all the ways to put the boxes, what’s the maximum number of boxes we can put in?
+</details>
+
+<details>
+<summary>Hint 2</summary>
+The first box should always start in the corner
+</details>

problems/building-boxes/README.md

@@ -13,7 +13,7 @@
 
 <p>You are given <code>n</code> balloons, indexed from <code>0</code> to <code>n - 1</code>. Each balloon is painted with a number on it represented by an array <code>nums</code>. You are asked to burst all the balloons.</p>
 
-<p>If you burst the <code>i<sup>th</sup></code> balloon, you will get <code>nums[left] * nums[i] * nums[right]</code> coins. Here <code>left</code> and <code>right</code> are adjacent indices of <code>i</code>. After the burst, the <code>left</code> and <code>right</code> then becomes adjacent.</p>
+<p>If you burst the <code>i<sup>th</sup></code> balloon, you will get <code>nums[i - 1] * nums[i] * nums[i + 1]</code> coins. If <code>i - 1</code> or <code>i + 1</code> goes out of bounds of the array, then treat it as if there is a balloon with a <code>1</code> painted on it.</p>
 
 <p>Return <em>the maximum coins you can collect by bursting the balloons wisely</em>.</p>
 
@@ -23,8 +23,8 @@
 <pre>
 <strong>Input:</strong> nums = [3,1,5,8]
 <strong>Output:</strong> 167
-<code><strong>Explanation:
-</strong></code>nums = [3,1,5,8] --&gt; [3,5,8] --&gt; [3,8] --&gt; [8] --&gt; []
+<strong>Explanation:</strong>
+nums = [3,1,5,8] --&gt; [3,5,8] --&gt; [3,8] --&gt; [8] --&gt; []
 coins =  3*1*5    +   3*5*8   +  1*3*8  + 1*8*1 = 167</pre>
 
 <p><strong>Example 2:</strong></p>