A: new

README.md

@@ -62,6 +62,11 @@ LeetCode Problems' Solutions
 
 | # | Title | Solution | Difficulty |
 | :-: | - | - | :-: |
+| <span id="1444">1444</span> | [Number of Ways of Cutting a Pizza](https://leetcode.com/problems/number-of-ways-of-cutting-a-pizza "切披萨的方案数") | [Go](problems/number-of-ways-of-cutting-a-pizza) | Hard |
+| <span id="1443">1443</span> | [Minimum Time to Collect All Apples in a Tree](https://leetcode.com/problems/minimum-time-to-collect-all-apples-in-a-tree "收集树上所有苹果的最少时间") | [Go](problems/minimum-time-to-collect-all-apples-in-a-tree) | Medium |
+| <span id="1442">1442</span> | [Count Triplets That Can Form Two Arrays of Equal XOR](https://leetcode.com/problems/count-triplets-that-can-form-two-arrays-of-equal-xor "形成两个异或相等数组的三元组数目") | [Go](problems/count-triplets-that-can-form-two-arrays-of-equal-xor) | Medium |
+| <span id="1441">1441</span> | [Build an Array With Stack Operations](https://leetcode.com/problems/build-an-array-with-stack-operations "用栈操作构建数组") | [Go](problems/build-an-array-with-stack-operations) | Easy |
+| <span id="1440">1440</span> | [Evaluate Boolean Expression](https://leetcode.com/problems/evaluate-boolean-expression) 🔒 | [MySQL](problems/evaluate-boolean-expression) | Medium |
 | <span id="1439">1439</span> | [Find the Kth Smallest Sum of a Matrix With Sorted Rows](https://leetcode.com/problems/find-the-kth-smallest-sum-of-a-matrix-with-sorted-rows "有序矩阵中的第 k 个最小数组和") | [Go](problems/find-the-kth-smallest-sum-of-a-matrix-with-sorted-rows) | Hard |
 | <span id="1438">1438</span> | [Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit](https://leetcode.com/problems/longest-continuous-subarray-with-absolute-diff-less-than-or-equal-to-limit "绝对差不超过限制的最长连续子数组") | [Go](problems/longest-continuous-subarray-with-absolute-diff-less-than-or-equal-to-limit) | Medium |
 | <span id="1437">1437</span> | [Check If All 1's Are at Least Length K Places Away](https://leetcode.com/problems/check-if-all-1s-are-at-least-length-k-places-away "是否所有 1 都至少相隔 k 个元素") | [Go](problems/check-if-all-1s-are-at-least-length-k-places-away) | Medium |

problems/build-an-array-with-stack-operations/README.md

@@ -0,0 +1,81 @@
+<!--|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](../evaluate-boolean-expression "Evaluate Boolean Expression")
+
+[Next >](../count-triplets-that-can-form-two-arrays-of-equal-xor "Count Triplets That Can Form Two Arrays of Equal XOR")
+
+## [1441. Build an Array With Stack Operations (Easy)](https://leetcode.com/problems/build-an-array-with-stack-operations "用栈操作构建数组")
+
+<p>Given an array <code>target</code> and&nbsp;an integer <code>n</code>. In each iteration, you will read a number from &nbsp;<code>list = {1,2,3..., n}</code>.</p>
+
+<p>Build the <code>target</code>&nbsp;array&nbsp;using the following operations:</p>
+
+<ul>
+	<li><strong>Push</strong>: Read a new element from the beginning&nbsp;<code>list</code>, and push it in the array.</li>
+	<li><strong>Pop</strong>: delete the last element of&nbsp;the array.</li>
+	<li>If the target array is already&nbsp;built, stop reading more elements.</li>
+</ul>
+
+<p>You are guaranteed that the target array is strictly&nbsp;increasing, only containing&nbsp;numbers between 1 to <code>n</code>&nbsp;inclusive.</p>
+
+<p>Return the operations to build the target array.</p>
+
+<p>You are guaranteed that the answer is unique.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,3], n = 3
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;,&quot;Pop&quot;,&quot;Push&quot;]
+<strong>Explanation: 
+</strong>Read number 1 and automatically push in the array -&gt; [1]
+Read number 2 and automatically push in the array then Pop it -&gt; [1]
+Read number 3 and automatically push in the array -&gt; [1,3]
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,2,3], n = 3
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;,&quot;Push&quot;]
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,2], n = 4
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;]
+<strong>Explanation: </strong>You only need to read the first 2 numbers and stop.
+</pre>
+
+<p><strong>Example 4:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [2,3,4], n = 4
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Pop&quot;,&quot;Push&quot;,&quot;Push&quot;,&quot;Push&quot;]
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= target.length &lt;= 100</code></li>
+	<li><code>1 &lt;= target[i]&nbsp;&lt;= 100</code></li>
+	<li><code>1 &lt;= n &lt;= 100</code></li>
+	<li><code>target</code> is strictly&nbsp;increasing.</li>
+</ul>
+
+### Related Topics
+  [[Stack](../../tag/stack/README.md)]
+
+### Hints
+<details>
+<summary>Hint 1</summary>
+Use “Push” for numbers to be kept in target array and [“Push”, “Pop”] for numbers to be discarded.
+</details>

problems/count-triplets-that-can-form-two-arrays-of-equal-xor/README.md

@@ -0,0 +1,88 @@
+<!--|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](../build-an-array-with-stack-operations "Build an Array With Stack Operations")
+
+[Next >](../minimum-time-to-collect-all-apples-in-a-tree "Minimum Time to Collect All Apples in a Tree")
+
+## [1442. Count Triplets That Can Form Two Arrays of Equal XOR (Medium)](https://leetcode.com/problems/count-triplets-that-can-form-two-arrays-of-equal-xor "形成两个异或相等数组的三元组数目")
+
+<p>Given an array of&nbsp;integers <code>arr</code>.</p>
+
+<p>We want to select three indices <code>i</code>, <code>j</code> and <code>k</code> where <code>(0 &lt;= i &lt; j &lt;= k &lt; arr.length)</code>.</p>
+
+<p>Let&#39;s define <code>a</code> and <code>b</code> as follows:</p>
+
+<ul>
+	<li><code>a = arr[i] ^ arr[i + 1] ^ ... ^ arr[j - 1]</code></li>
+	<li><code>b = arr[j] ^ arr[j + 1] ^ ... ^ arr[k]</code></li>
+</ul>
+
+<p>Note that <strong>^</strong> denotes the <strong>bitwise-xor</strong> operation.</p>
+
+<p>Return <em>the number of triplets</em> (<code>i</code>, <code>j</code> and <code>k</code>) Where <code>a == b</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [2,3,1,6,7]
+<strong>Output:</strong> 4
+<strong>Explanation:</strong> The triplets are (0,1,2), (0,2,2), (2,3,4) and (2,4,4)
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [1,1,1,1,1]
+<strong>Output:</strong> 10
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [2,3]
+<strong>Output:</strong> 0
+</pre>
+
+<p><strong>Example 4:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [1,3,5,7,9]
+<strong>Output:</strong> 3
+</pre>
+
+<p><strong>Example 5:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [7,11,12,9,5,2,7,17,22]
+<strong>Output:</strong> 8
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= arr.length &lt;= 300</code></li>
+	<li><code>1 &lt;= arr[i] &lt;= 10^8</code></li>
+</ul>
+
+### Related Topics
+  [[Bit Manipulation](../../tag/bit-manipulation/README.md)]
+  [[Array](../../tag/array/README.md)]
+  [[Math](../../tag/math/README.md)]
+
+### Hints
+<details>
+<summary>Hint 1</summary>
+We are searching for sub-array of length ≥ 2 and we need to split it to 2 non-empty arrays so that the xor of the first array is equal to the xor of the second array. This is equivalent to searching for sub-array with xor = 0.
+</details>
+
+<details>
+<summary>Hint 2</summary>
+Keep the prefix xor of arr in another array, check the xor of all sub-arrays in O(n^2), if the xor of sub-array of length x is 0 add x-1 to the answer.
+</details>

problems/evaluate-boolean-expression/README.md

@@ -0,0 +1,14 @@
+<!--|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-the-kth-smallest-sum-of-a-matrix-with-sorted-rows "Find the Kth Smallest Sum of a Matrix With Sorted Rows")
+
+[Next >](../build-an-array-with-stack-operations "Build an Array With Stack Operations")
+
+## [1440. Evaluate Boolean Expression (Medium)](https://leetcode.com/problems/evaluate-boolean-expression "")
+
+

problems/evaluate-boolean-expression/mysql_schemas.sql

@@ -0,0 +1,12 @@
+Create Table If Not Exists Variables (name varchar(3), value int);
+Create Table If Not Exists Expressions (left_operand varchar(3), operator ENUM('>', '<', '='), right_operand varchar(3));
+Truncate table Variables;
+insert into Variables (name, value) values ('x', '66');
+insert into Variables (name, value) values ('y', '77');
+Truncate table Expressions;
+insert into Expressions (left_operand, operator, right_operand) values ('x', '>', 'y');
+insert into Expressions (left_operand, operator, right_operand) values ('x', '<', 'y');
+insert into Expressions (left_operand, operator, right_operand) values ('x', '=', 'y');
+insert into Expressions (left_operand, operator, right_operand) values ('y', '>', 'x');
+insert into Expressions (left_operand, operator, right_operand) values ('y', '<', 'x');
+insert into Expressions (left_operand, operator, right_operand) values ('x', '=', 'x');

problems/find-k-closest-elements/README.md

@@ -11,40 +11,24 @@
 
 ## [658. Find K Closest Elements (Medium)](https://leetcode.com/problems/find-k-closest-elements "找到 K 个最接近的元素")
 
-<p>
-Given a sorted array, two integers <code>k</code> and <code>x</code>, find the <code>k</code> closest elements to <code>x</code> in the array.  The result should also be sorted in ascending order.
-If there is a tie,  the smaller elements are always preferred.
-</p>
-
-<p><b>Example 1:</b><br />
-<pre>
-<b>Input:</b> [1,2,3,4,5], k=4, x=3
-<b>Output:</b> [1,2,3,4]
-</pre>
-</p>
-
-
-<p><b>Example 2:</b><br />
-<pre>
-<b>Input:</b> [1,2,3,4,5], k=4, x=-1
-<b>Output:</b> [1,2,3,4]
+<p>Given a sorted array <code>arr</code>, two integers <code>k</code> and <code>x</code>, find the <code>k</code> closest elements to <code>x</code> in the array. The result should also be sorted in ascending order. If there is a tie, the smaller elements are always preferred.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+<pre><strong>Input:</strong> arr = [1,2,3,4,5], k = 4, x = 3
+<strong>Output:</strong> [1,2,3,4]
+</pre><p><strong>Example 2:</strong></p>
+<pre><strong>Input:</strong> arr = [1,2,3,4,5], k = 4, x = -1
+<strong>Output:</strong> [1,2,3,4]
 </pre>
-</p>
-
-<p><b>Note:</b><br>
-<ol>
-<li>The value k is positive and will always be smaller than the length of the sorted array.</li>
-<li> Length of the given array is positive and will not exceed 10<sup>4</sup></li>
-<li> Absolute value of elements in the array and x will not exceed 10<sup>4</sup></li>
-</ol>
-</p>
-
-<hr />
-
-<p>
-<b><font color="red">UPDATE (2017/9/19):</font></b><br />
-The <i>arr</i> parameter had been changed to an <b>array of integers</b> (instead of a list of integers). <b><i>Please reload the code definition to get the latest changes</i></b>.
-</p>
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= k &lt;= arr.length</code></li>
+	<li><code>1 &lt;= arr.length&nbsp;&lt;= 10^4</code></li>
+	<li>Absolute value of elements in the array and <code>x</code> will not exceed 10<sup>4</sup></li>
+</ul>
 
 ### Related Topics
   [[Binary Search](../../tag/binary-search/README.md)]

problems/find-the-kth-smallest-sum-of-a-matrix-with-sorted-rows/README.md

@@ -7,7 +7,7 @@
 
 [< Previous](../longest-continuous-subarray-with-absolute-diff-less-than-or-equal-to-limit "Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit")
 
-Next >
+[Next >](../evaluate-boolean-expression "Evaluate Boolean Expression")
 
 ## [1439. Find the Kth Smallest Sum of a Matrix With Sorted Rows (Hard)](https://leetcode.com/problems/find-the-kth-smallest-sum-of-a-matrix-with-sorted-rows "有序矩阵中的第 k 个最小数组和")
 

problems/insert-into-a-binary-search-tree/README.md

@@ -49,6 +49,16 @@ And the value to insert: 5
           4
 </pre>
 
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li>The number of nodes in the given tree will be between <code>0</code> and <code>10^4</code>.</li>
+	<li>Each node will have a unique integer value from <code>0</code>&nbsp;to -<code>10^8</code>, inclusive.</li>
+	<li><code>-10^8 &lt;= val &lt;= 10^8</code></li>
+	<li>It&#39;s guaranteed that <code>val</code> does not exist in the original BST.</li>
+</ul>
+
 ### Related Topics
   [[Tree](../../tag/tree/README.md)]
 

problems/median-of-two-sorted-arrays/README.md

@@ -9,7 +9,7 @@
 
 [Next >](../longest-palindromic-substring "Longest Palindromic Substring")
 
-## [4. Median of Two Sorted Arrays (Hard)](https://leetcode.com/problems/median-of-two-sorted-arrays "寻找两个有序数组的中位数")
+## [4. Median of Two Sorted Arrays (Hard)](https://leetcode.com/problems/median-of-two-sorted-arrays "寻找两个正序数组的中位数")
 
 <p>There are two sorted arrays <b>nums1</b> and <b>nums2</b> of size m and n respectively.</p>