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16 changes: 16 additions & 0 deletions README.md
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Expand Up @@ -78,6 +78,22 @@ LeetCode Problems' Solutions

| # | Title | Solution | Difficulty |
| :-: | - | - | :-: |
| <span id="1819">1819</span> | [Number of Different Subsequences GCDs](https://leetcode.com/problems/number-of-different-subsequences-gcds "序列中不同最大公约数的数目") | [Go](problems/number-of-different-subsequences-gcds) | Hard |
| <span id="1818">1818</span> | [Minimum Absolute Sum Difference](https://leetcode.com/problems/minimum-absolute-sum-difference "绝对差值和") | [Go](problems/minimum-absolute-sum-difference) | Medium |
| <span id="1817">1817</span> | [Finding the Users Active Minutes](https://leetcode.com/problems/finding-the-users-active-minutes "查找用户活跃分钟数") | [Go](problems/finding-the-users-active-minutes) | Medium |
| <span id="1816">1816</span> | [Truncate Sentence](https://leetcode.com/problems/truncate-sentence "截断句子") | [Go](problems/truncate-sentence) | Easy |
| <span id="1815">1815</span> | [Maximum Number of Groups Getting Fresh Donuts](https://leetcode.com/problems/maximum-number-of-groups-getting-fresh-donuts "得到新鲜甜甜圈的最多组数") | [Go](problems/maximum-number-of-groups-getting-fresh-donuts) | Hard |
| <span id="1814">1814</span> | [Count Nice Pairs in an Array](https://leetcode.com/problems/count-nice-pairs-in-an-array "统计一个数组中好对子的数目") | [Go](problems/count-nice-pairs-in-an-array) | Medium |
| <span id="1813">1813</span> | [Sentence Similarity III](https://leetcode.com/problems/sentence-similarity-iii "句子相似性 III") | [Go](problems/sentence-similarity-iii) | Medium |
| <span id="1812">1812</span> | [Determine Color of a Chessboard Square](https://leetcode.com/problems/determine-color-of-a-chessboard-square "判断国际象棋棋盘中一个格子的颜色") | [Go](problems/determine-color-of-a-chessboard-square) | Easy |
| <span id="1811">1811</span> | [Find Interview Candidates](https://leetcode.com/problems/find-interview-candidates) 🔒 | [MySQL](problems/find-interview-candidates) | Medium |
| <span id="1810">1810</span> | [Minimum Path Cost in a Hidden Grid](https://leetcode.com/problems/minimum-path-cost-in-a-hidden-grid) 🔒 | [Go](problems/minimum-path-cost-in-a-hidden-grid) | Medium |
| <span id="1809">1809</span> | [Ad-Free Sessions](https://leetcode.com/problems/ad-free-sessions) 🔒 | [MySQL](problems/ad-free-sessions) | Easy |
| <span id="1808">1808</span> | [Maximize Number of Nice Divisors](https://leetcode.com/problems/maximize-number-of-nice-divisors "好因子的最大数目") | [Go](problems/maximize-number-of-nice-divisors) | Hard |
| <span id="1807">1807</span> | [Evaluate the Bracket Pairs of a String](https://leetcode.com/problems/evaluate-the-bracket-pairs-of-a-string "替换字符串中的括号内容") | [Go](problems/evaluate-the-bracket-pairs-of-a-string) | Medium |
| <span id="1806">1806</span> | [Minimum Number of Operations to Reinitialize a Permutation](https://leetcode.com/problems/minimum-number-of-operations-to-reinitialize-a-permutation "还原排列的最少操作步数") | [Go](problems/minimum-number-of-operations-to-reinitialize-a-permutation) | Medium |
| <span id="1805">1805</span> | [Number of Different Integers in a String](https://leetcode.com/problems/number-of-different-integers-in-a-string "字符串中不同整数的数目") | [Go](problems/number-of-different-integers-in-a-string) | Easy |
| <span id="1804">1804</span> | [Implement Trie II (Prefix Tree)](https://leetcode.com/problems/implement-trie-ii-prefix-tree) 🔒 | [Go](problems/implement-trie-ii-prefix-tree) | Medium |
| <span id="1803">1803</span> | [Count Pairs With XOR in a Range](https://leetcode.com/problems/count-pairs-with-xor-in-a-range "统计异或值在范围内的数对有多少") | [Go](problems/count-pairs-with-xor-in-a-range) | Hard |
| <span id="1802">1802</span> | [Maximum Value at a Given Index in a Bounded Array](https://leetcode.com/problems/maximum-value-at-a-given-index-in-a-bounded-array "有界数组中指定下标处的最大值") | [Go](problems/maximum-value-at-a-given-index-in-a-bounded-array) | Medium |
| <span id="1801">1801</span> | [Number of Orders in the Backlog](https://leetcode.com/problems/number-of-orders-in-the-backlog "积压订单中的订单总数") | [Go](problems/number-of-orders-in-the-backlog) | Medium |
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2 changes: 1 addition & 1 deletion problems/132-pattern/README.md
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[Next >](../circular-array-loop "Circular Array Loop")

## [456. 132 Pattern (Medium)](https://leetcode.com/problems/132-pattern "132模式")
## [456. 132 Pattern (Medium)](https://leetcode.com/problems/132-pattern "132 模式")

<p>Given an array&nbsp;of <code>n</code> integers <code>nums</code>, a <strong>132 pattern</strong> is a subsequence of three integers <code>nums[i]</code>, <code>nums[j]</code> and <code>nums[k]</code> such that <code>i &lt; j &lt; k</code> and <code>nums[i] &lt; nums[k] &lt; nums[j]</code>.</p>

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2 changes: 1 addition & 1 deletion problems/3sum/README.md
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## [15. 3Sum (Medium)](https://leetcode.com/problems/3sum "三数之和")

<p>Given an array <code>nums</code> of <em>n</em> integers, are there elements <em>a</em>, <em>b</em>, <em>c</em> in <code>nums</code> such that <em>a</em> + <em>b</em> + <em>c</em> = 0? Find all unique triplets in the array which gives the sum of zero.</p>
<p>Given an integer array nums, return all the triplets <code>[nums[i], nums[j], nums[k]]</code> such that <code>i != j</code>, <code>i != k</code>, and <code>j != k</code>, and <code>nums[i] + nums[j] + nums[k] == 0</code>.</p>

<p>Notice that the solution set must not contain duplicate triplets.</p>

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14 changes: 14 additions & 0 deletions problems/ad-free-sessions/README.md
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<!--|This file generated by command(leetcode description); DO NOT EDIT. |-->
<!--+----------------------------------------------------------------------+-->
<!--|@author openset <openset.wang@gmail.com> |-->
<!--|@link https://github.com/openset |-->
<!--|@home https://github.com/openset/leetcode |-->
<!--+----------------------------------------------------------------------+-->

[< Previous](../maximize-number-of-nice-divisors "Maximize Number of Nice Divisors")

[Next >](../minimum-path-cost-in-a-hidden-grid "Minimum Path Cost in a Hidden Grid")

## [1809. Ad-Free Sessions (Easy)](https://leetcode.com/problems/ad-free-sessions "")


12 changes: 12 additions & 0 deletions problems/ad-free-sessions/mysql_schemas.sql
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Create table If Not Exists Playback(session_id int,customer_id int,start_time int,end_time int);
Create table If Not Exists Ads (ad_id int, customer_id int, timestamp int);
Truncate table Playback;
insert into Playback (session_id, customer_id, start_time, end_time) values ('1', '1', '1', '5');
insert into Playback (session_id, customer_id, start_time, end_time) values ('2', '1', '15', '23');
insert into Playback (session_id, customer_id, start_time, end_time) values ('3', '2', '10', '12');
insert into Playback (session_id, customer_id, start_time, end_time) values ('4', '2', '17', '28');
insert into Playback (session_id, customer_id, start_time, end_time) values ('5', '2', '2', '8');
Truncate table Ads;
insert into Ads (ad_id, customer_id, timestamp) values ('1', '1', '5');
insert into Ads (ad_id, customer_id, timestamp) values ('2', '2', '17');
insert into Ads (ad_id, customer_id, timestamp) values ('3', '2', '20');
45 changes: 35 additions & 10 deletions problems/add-strings/README.md
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## [415. Add Strings (Easy)](https://leetcode.com/problems/add-strings "字符串相加")

<p>Given two non-negative integers <code>num1</code> and <code>num2</code> represented as string, return the sum of <code>num1</code> and <code>num2</code>.</p>

<p><b>Note:</b>
<ol>
<li>The length of both <code>num1</code> and <code>num2</code> is < 5100.</li>
<li>Both <code>num1</code> and <code>num2</code> contains only digits <code>0-9</code>.</li>
<li>Both <code>num1</code> and <code>num2</code> does not contain any leading zero.</li>
<li>You <b>must not use any built-in BigInteger library</b> or <b>convert the inputs to integer</b> directly.</li>
</ol>
</p>
<p>Given two non-negative integers, <code>num1</code> and <code>num2</code> represented as string, return <em>the sum of</em> <code>num1</code> <em>and</em> <code>num2</code> <em>as a string</em>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> num1 = &quot;11&quot;, num2 = &quot;123&quot;
<strong>Output:</strong> &quot;134&quot;
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> num1 = &quot;456&quot;, num2 = &quot;77&quot;
<strong>Output:</strong> &quot;533&quot;
</pre>

<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong> num1 = &quot;0&quot;, num2 = &quot;0&quot;
<strong>Output:</strong> &quot;0&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
<li><code>1 &lt;= num1.length, num2.length &lt;= 10<sup>4</sup></code></li>
<li><code>num1</code> and <code>num2</code> consist of only digits.</li>
<li><code>num1</code> and <code>num2</code> don&#39;t have any leading zeros except for the zero itself.</li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up:</strong> Could you solve it without using any built-in <code>BigInteger</code> library or converting the inputs to integer directly?</p>

### Related Topics
[[String](../../tag/string/README.md)]
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61 changes: 26 additions & 35 deletions problems/add-to-array-form-of-integer/README.md
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## [989. Add to Array-Form of Integer (Easy)](https://leetcode.com/problems/add-to-array-form-of-integer "数组形式的整数加法")

<p>For a non-negative integer <code>X</code>, the&nbsp;<em>array-form of <code>X</code></em>&nbsp;is an array of its digits in left to right order.&nbsp; For example, if <code>X = 1231</code>, then the array form is&nbsp;<code>[1,2,3,1]</code>.</p>
<p>The <strong>array-form</strong> of an integer <code>num</code>is an array representing its digits in left to right order.</p>

<p>Given the array-form <code>A</code> of a non-negative&nbsp;integer <code>X</code>, return the array-form of the integer <code>X+K</code>.</p>
<ul>
<li>For example, for <code>num = 1321</code>, the array form is <code>[1,3,2,1]</code>.</li>
</ul>

<p>&nbsp;</p>

<ol>
</ol>
<p>Given <code>num</code>, the <strong>array-form</strong> of an integer, and an integer <code>k</code>, return <em>the <strong>array-form</strong> of the integer</em> <code>num + k</code>.</p>

<div>
<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong>A = <span id="example-input-1-1">[1,2,0,0]</span>, K = 34
<strong>Output:</strong><span id="example-output-1">[1,2,3,4]</span>
<strong>Explanation:</strong>1200 + 34 = 1234
<strong>Input:</strong> num = [1,2,0,0], k = 34
<strong>Output:</strong>[1,2,3,4]
<strong>Explanation:</strong>1200 + 34 = 1234
</pre>

<div>
<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong>A = <span id="example-input-2-1">[2,7,4]</span>, K = <span id="example-input-2-2">181</span>
<strong>Output:</strong><span id="example-output-2">[4,5,5]</span>
<strong>Explanation:</strong>274 + 181 = 455
<strong>Input:</strong> num = [2,7,4], k = 181
<strong>Output:</strong>[4,5,5]
<strong>Explanation:</strong>274 + 181 = 455
</pre>

<div>
<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong>A = <span id="example-input-3-1">[2,1,5]</span>, K = <span id="example-input-3-2">806</span>
<strong>Output:</strong><span id="example-output-3">[1,0,2,1]</span>
<strong>Explanation:</strong>215 + 806 = 1021
<strong>Input:</strong> num = [2,1,5], k = 806
<strong>Output:</strong>[1,0,2,1]
<strong>Explanation:</strong>215 + 806 = 1021
</pre>

<div>
<p><strong>Example 4:</strong></p>

<pre>
<strong>Input:</strong>A = <span id="example-input-4-1">[9,9,9,9,9,9,9,9,9,9]</span>, K = <span id="example-input-4-2">1</span>
<strong>Output:</strong><span id="example-output-4">[1,0,0,0,0,0,0,0,0,0,0]</span>
<strong>Explanation:</strong>9999999999 +たす 1 =わ 10000000000
<strong>Input:</strong> num = [9,9,9,9,9,9,9,9,9,9], k = 1
<strong>Output:</strong>[1,0,0,0,0,0,0,0,0,0,0]
<strong>Explanation:</strong>9999999999 +たす 1 =わ 10000000000
</pre>

<p>&nbsp;</p>

<p><strong>Note:</strong></p>

<ol>
<li><code>1 &lt;= A.length &lt;= 10000</code></li>
<li><code>0 &lt;= A[i] &lt;= 9</code></li>
<li><code>0 &lt;= K &lt;= 10000</code></li>
<li>If <code>A.length &gt; 1</code>, then <code>A[0] != 0</code></li>
</ol>
</div>
</div>
</div>
</div>
<p><strong>Constraints:</strong></p>

<ul>
<li><code>1 &lt;= num.length &lt;= 10<sup>4</sup></code></li>
<li><code>0 &lt;= num[i] &lt;= 9</code></li>
<li><code>num</code>&nbsp;does not contain any leading zeros except for the zero itself.</li>
<li><code>1 &lt;= k &lt;= 10<sup>4</sup></code></li>
</ul>

### Related Topics
[[Array](../../tag/array/README.md)]
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2 changes: 1 addition & 1 deletion problems/candy/README.md
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Expand Up @@ -46,7 +46,7 @@ The third child gets 1 candy because it satisfies the above two conditions.
<ul>
<li><code>n == ratings.length</code></li>
<li><code>1 &lt;= n &lt;= 2 * 10<sup>4</sup></code></li>
<li><code>1 &lt;= ratings[i] &lt;= 2 * 10<sup>4</sup></code></li>
<li><code>0 &lt;= ratings[i] &lt;= 2 * 10<sup>4</sup></code></li>
</ul>

### Related Topics
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2 changes: 1 addition & 1 deletion problems/combinations/README.md
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## [77. Combinations (Medium)](https://leetcode.com/problems/combinations "组合")

<p>Given two integers <em>n</em> and <em>k</em>, return all possible combinations of <em>k</em> numbers out of 1 ... <em>n</em>.</p>
<p>Given two integers <code>n</code> and <code>k</code>, return <em>all possible combinations of</em> <code>k</code> <em>numbers out of the range</em> <code>[1, n]</code>.</p>

<p>You may return the answer in <strong>any order</strong>.</p>

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33 changes: 22 additions & 11 deletions problems/continuous-subarray-sum/README.md
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## [523. Continuous Subarray Sum (Medium)](https://leetcode.com/problems/continuous-subarray-sum "连续的子数组和")

<p>Given a list of <b>non-negative</b> numbers and a target <b>integer</b> k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to a multiple of <b>k</b>, that is, sums up to n*k where n is also an <b>integer</b>.</p>
<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <code>true</code> <em>if </em><code>nums</code><em> has a continuous subarray of size <strong>at least two</strong> whose elements sum up to a multiple of</em> <code>k</code><em>, or </em><code>false</code><em> otherwise</em>.</p>

<p>An integer <code>x</code> is a multiple of <code>k</code> if there exists an integer <code>n</code> such that <code>x = n * k</code>. <code>0</code> is <strong>always</strong> a multiple of <code>k</code>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [23,<u>2,4</u>,6,7], k = 6
<strong>Output:</strong> true
<strong>Explanation:</strong> [2, 4] is a continuous subarray of size 2 whose elements sum up to 6.
</pre>

<p><b>Example 1:</b></p>
<p><strong>Example 2:</strong></p>

<pre>
<b>Input:</b> [23, 2, 4, 6, 7], k=6
<b>Output:</b> True
<b>Explanation:</b> Because [2, 4] is a continuous subarray of size 2 and sums up to 6.
<strong>Input:</strong> nums = [<u>23,2,6,4,7</u>], k = 6
<strong>Output:</strong> true
<strong>Explanation:</strong> [23, 2, 6, 4, 7] is an continuous subarray of size 5 whose elements sum up to 42.
42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer.
</pre>

<p><b>Example 2:</b></p>
<p><strong>Example 3:</strong></p>

<pre>
<b>Input:</b> [23, 2, 6, 4, 7], k=6
<b>Output:</b> True
<b>Explanation:</b> Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42.
<strong>Input:</strong> nums = [23,2,6,4,7], k = 13
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
<li>The length of the array won&#39;t exceed 10,000.</li>
<li>You may assume the sum of all the numbers is in the range of a signed 32-bit integer.</li>
<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
<li><code>0 &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
<li><code>0 &lt;= sum(nums[i]) &lt;= 2<sup>31</sup> - 1</code></li>
<li><code>1 &lt;= k &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

### Related Topics
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67 changes: 67 additions & 0 deletions problems/count-nice-pairs-in-an-array/README.md
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<!--|This file generated by command(leetcode description); DO NOT EDIT. |-->
<!--+----------------------------------------------------------------------+-->
<!--|@author openset <openset.wang@gmail.com> |-->
<!--|@link https://github.com/openset |-->
<!--|@home https://github.com/openset/leetcode |-->
<!--+----------------------------------------------------------------------+-->

[< Previous](../sentence-similarity-iii "Sentence Similarity III")

[Next >](../maximum-number-of-groups-getting-fresh-donuts "Maximum Number of Groups Getting Fresh Donuts")

## [1814. Count Nice Pairs in an Array (Medium)](https://leetcode.com/problems/count-nice-pairs-in-an-array "统计一个数组中好对子的数目")

<p>You are given an array <code>nums</code> that consists of non-negative integers. Let us define <code>rev(x)</code> as the reverse of the non-negative integer <code>x</code>. For example, <code>rev(123) = 321</code>, and <code>rev(120) = 21</code>. A pair of indices <code>(i, j)</code> is <strong>nice</strong> if it satisfies all of the following conditions:</p>

<ul>
<li><code>0 &lt;= i &lt; j &lt; nums.length</code></li>
<li><code>nums[i] + rev(nums[j]) == nums[j] + rev(nums[i])</code></li>
</ul>

<p>Return <em>the number of nice pairs of indices</em>. Since that number can be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [42,11,1,97]
<strong>Output:</strong> 2
<strong>Explanation:</strong> The two pairs are:
- (0,3) : 42 + rev(97) = 42 + 79 = 121, 97 + rev(42) = 97 + 24 = 121.
- (1,2) : 11 + rev(1) = 11 + 1 = 12, 1 + rev(11) = 1 + 11 = 12.
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [13,10,35,24,76]
<strong>Output:</strong> 4
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
<li><code>0 &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
</ul>

### Related Topics
[[Array](../../tag/array/README.md)]
[[Hash Table](../../tag/hash-table/README.md)]

### Hints
<details>
<summary>Hint 1</summary>
The condition can be rearranged to (nums[i] - rev(nums[i])) == (nums[j] - rev(nums[j])).
</details>

<details>
<summary>Hint 2</summary>
Transform each nums[i] into (nums[i] - rev(nums[i])). Then, count the number of (i, j) pairs that have equal values.
</details>

<details>
<summary>Hint 3</summary>
Keep a map storing the frequencies of values that you have seen so far. For each i, check if nums[i] is in the map. If it is, then add that count to the overall count. Then, increment the frequency of nums[i].
</details>
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