feat: add weekly contest 472

solution/3700-3799/3707.Equal Score Substrings/README.md

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 comments: true
 difficulty: 简单
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3707.Equal%20Score%20Substrings/README.md
+rating: 1262
+source: 第 167 场双周赛 Q1
 ---
 
 <!-- problem:start -->

solution/3700-3799/3707.Equal Score Substrings/README_EN.md

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 comments: true
 difficulty: Easy
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3707.Equal%20Score%20Substrings/README_EN.md
+rating: 1262
+source: Biweekly Contest 167 Q1
 ---
 
 <!-- problem:start -->

solution/3700-3799/3708.Longest Fibonacci Subarray/README.md

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 comments: true
 difficulty: 中等
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3708.Longest%20Fibonacci%20Subarray/README.md
+rating: 1380
+source: 第 167 场双周赛 Q2
 ---
 
 <!-- problem:start -->

solution/3700-3799/3708.Longest Fibonacci Subarray/README_EN.md

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 comments: true
 difficulty: Medium
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3708.Longest%20Fibonacci%20Subarray/README_EN.md
+rating: 1380
+source: Biweekly Contest 167 Q2
 ---
 
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solution/3700-3799/3709.Design Exam Scores Tracker/README.md

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 comments: true
 difficulty: 中等
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3709.Design%20Exam%20Scores%20Tracker/README.md
+rating: 1647
+source: 第 167 场双周赛 Q3
 ---
 
 <!-- problem:start -->

solution/3700-3799/3709.Design Exam Scores Tracker/README_EN.md

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 comments: true
 difficulty: Medium
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3709.Design%20Exam%20Scores%20Tracker/README_EN.md
+rating: 1647
+source: Biweekly Contest 167 Q3
 ---
 
 <!-- problem:start -->

solution/3700-3799/3710.Maximum Partition Factor/README.md

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 comments: true
 difficulty: 困难
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3710.Maximum%20Partition%20Factor/README.md
+rating: 2135
+source: 第 167 场双周赛 Q4
 ---
 
 <!-- problem:start -->

solution/3700-3799/3710.Maximum Partition Factor/README_EN.md

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 comments: true
 difficulty: Hard
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3710.Maximum%20Partition%20Factor/README_EN.md
+rating: 2135
+source: Biweekly Contest 167 Q4
 ---
 
 <!-- problem:start -->

solution/3700-3799/3712.Sum of Elements With Frequency Divisible by K/README.md

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 comments: true
 difficulty: 简单
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3712.Sum%20of%20Elements%20With%20Frequency%20Divisible%20by%20K/README.md
+rating: 1198
+source: 第 471 场周赛 Q1
 ---
 
 <!-- problem:start -->

solution/3700-3799/3712.Sum of Elements With Frequency Divisible by K/README_EN.md

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 comments: true
 difficulty: Easy
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3712.Sum%20of%20Elements%20With%20Frequency%20Divisible%20by%20K/README_EN.md
+rating: 1198
+source: Weekly Contest 471 Q1
 ---
 
 <!-- problem:start -->

solution/3700-3799/3713.Longest Balanced Substring I/README.md

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 comments: true
 difficulty: 中等
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3713.Longest%20Balanced%20Substring%20I/README.md
+rating: 1490
+source: 第 471 场周赛 Q2
 ---
 
 <!-- problem:start -->

solution/3700-3799/3713.Longest Balanced Substring I/README_EN.md

@@ -2,6 +2,8 @@
 comments: true
 difficulty: Medium
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3713.Longest%20Balanced%20Substring%20I/README_EN.md
+rating: 1490
+source: Weekly Contest 471 Q2
 ---
 
 <!-- problem:start -->

solution/3700-3799/3714.Longest Balanced Substring II/README.md

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 comments: true
 difficulty: 中等
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3714.Longest%20Balanced%20Substring%20II/README.md
+rating: 2201
+source: 第 471 场周赛 Q3
 ---
 
 <!-- problem:start -->

solution/3700-3799/3714.Longest Balanced Substring II/README_EN.md

@@ -2,6 +2,8 @@
 comments: true
 difficulty: Medium
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3714.Longest%20Balanced%20Substring%20II/README_EN.md
+rating: 2201
+source: Weekly Contest 471 Q3
 ---
 
 <!-- problem:start -->

solution/3700-3799/3715.Sum of Perfect Square Ancestors/README.md

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 comments: true
 difficulty: 困难
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3715.Sum%20of%20Perfect%20Square%20Ancestors/README.md
+rating: 2235
+source: 第 471 场周赛 Q4
 ---
 
 <!-- problem:start -->

solution/3700-3799/3715.Sum of Perfect Square Ancestors/README_EN.md

@@ -2,6 +2,8 @@
 comments: true
 difficulty: Hard
 edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3715.Sum%20of%20Perfect%20Square%20Ancestors/README_EN.md
+rating: 2235
+source: Weekly Contest 471 Q4
 ---
 
 <!-- problem:start -->

solution/3700-3799/3716.Find Churn Risk Customers/README.md

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+---
+comments: true
+difficulty: 中等
+edit_url: https://github.com/doocs/leetcode/edit/main/solution/3700-3799/3716.Find%20Churn%20Risk%20Customers/README.md
+tags:
+    - 数据库
+---
+
+<!-- problem:start -->
+
+# [3716. 寻找流失风险客户](https://leetcode.cn/problems/find-churn-risk-customers)
+
+[English Version](/solution/3700-3799/3716.Find%20Churn%20Risk%20Customers/README_EN.md)
+
+## 题目描述
+
+<!-- description:start -->
+
+<p>表：<code>subscription_events</code></p>
+
+<pre>
++------------------+---------+
+| Column Name      | Type    | 
++------------------+---------+
+| event_id         | int     |
+| user_id          | int     |
+| event_date       | date    |
+| event_type       | varchar |
+| plan_name        | varchar |
+| monthly_amount   | decimal |
++------------------+---------+
+event_id 是这张表的唯一主键。
+event_type 可以是 start，upgrade，downgrade 或 cancel。
+plan_name 可以是 basic，standard，premium 或 NULL（当 event_type 是 cancel）。
+monthly_amount 表示此次事件后的月度订阅费用。
+对于 cancel 的事件，monthly_amount 为 0。
+</pre>
+
+<p>编写一个解决方案来 <strong>寻找流失风险用户</strong>&nbsp;- 出现预流失信号的用户。如果用户符合以下所有条件，则被视为 <strong>有流失风险</strong> 的客户：</p>
+
+<ul>
+	<li>目前有 <strong>有效的订阅</strong>（他们的最后事件不是 cancel）。</li>
+	<li>已在其订阅历史中 <strong>至少进行过一次</strong> 降级。</li>
+	<li>他们 <strong>目前的订阅费用</strong> 低于历史最高订阅费用的 <code>50%</code>。</li>
+	<li>已订阅 <strong>至少</strong> <code>60</code> 天。</li>
+</ul>
+
+<p>返回结果表按&nbsp;<code>days_as_subscriber</code> <strong>降序</strong>&nbsp;排序，然后按&nbsp;<code>user_id</code> <strong>升序&nbsp;</strong>排序。</p>
+
+<p>结果格式如下所示。</p>
+
+<p>&nbsp;</p>
+
+<p><strong class="example">示例：</strong></p>
+
+<div class="example-block">
+<p><strong>输入：</strong></p>
+
+<p>subscription_events 表：</p>
+
+<pre class="example-io">
++----------+---------+------------+------------+-----------+----------------+
+| event_id | user_id | event_date | event_type | plan_name | monthly_amount |
++----------+---------+------------+------------+-----------+----------------+
+| 1        | 501     | 2024-01-01 | start      | premium   | 29.99          |
+| 2        | 501     | 2024-02-15 | downgrade  | standard  | 19.99          |
+| 3        | 501     | 2024-03-20 | downgrade  | basic     | 9.99           |
+| 4        | 502     | 2024-01-05 | start      | standard  | 19.99          |
+| 5        | 502     | 2024-02-10 | upgrade    | premium   | 29.99          |
+| 6        | 502     | 2024-03-15 | downgrade  | basic     | 9.99           |
+| 7        | 503     | 2024-01-10 | start      | basic     | 9.99           |
+| 8        | 503     | 2024-02-20 | upgrade    | standard  | 19.99          |
+| 9        | 503     | 2024-03-25 | upgrade    | premium   | 29.99          |
+| 10       | 504     | 2024-01-15 | start      | premium   | 29.99          |
+| 11       | 504     | 2024-03-01 | downgrade  | standard  | 19.99          |
+| 12       | 504     | 2024-03-30 | cancel     | NULL      | 0.00           |
+| 13       | 505     | 2024-02-01 | start      | basic     | 9.99           |
+| 14       | 505     | 2024-02-28 | upgrade    | standard  | 19.99          |
+| 15       | 506     | 2024-01-20 | start      | premium   | 29.99          |
+| 16       | 506     | 2024-03-10 | downgrade  | basic     | 9.99           |
++----------+---------+------------+------------+-----------+----------------+
+</pre>
+
+<p><strong>输出：</strong></p>
+
+<pre class="example-io">
++----------+--------------+------------------------+-----------------------+--------------------+
+| user_id  | current_plan | current_monthly_amount | max_historical_amount | days_as_subscriber |
++----------+--------------+------------------------+-----------------------+--------------------+
+| 501      | basic        | 9.99                   | 29.99                 | 79                 |
+| 502      | basic        | 9.99                   | 29.99                 | 69                 |
++----------+--------------+------------------------+-----------------------+--------------------+
+</pre>
+
+<p><strong>解释：</strong></p>
+
+<ul>
+	<li><strong>用户 501：</strong>
+
+    <ul>
+    	<li>当前订阅有效：最近一次事件是降级到基础（未取消）</li>
+    	<li>有降级记录：是，历史上有 2 次降级</li>
+    	<li>当前订阅（9.99）vs 最大订阅（29.99）：9.99/29.99 = 33.3%（少于 50%）</li>
+    	<li>订阅天数：1 月 1 日到 5 月 20 日 = 79 天（至少 60 天）</li>
+    	<li>结果：<strong>流失风险客户</strong></li>
+    </ul>
+    </li>
+    <li><strong>用户 502：</strong>
+    <ul>
+    	<li>当前订阅有效：最近一次事件是降级到基础（未取消）</li>
+    	<li>有降级记录：是，历史上有 1 次降级</li>
+    	<li>当前订阅（9.99）vs 最大订阅（29.99）：9.99/29.99 = 33.3%（少于 50%）</li>
+    	<li>订阅天数：1 月&nbsp;5 日到 5 月 15 日 = 70 天（至少 60 天）</li>
+    	<li>结果：<strong>流失风险客户</strong></li>
+    </ul>
+    </li>
+    <li><strong>用户 503：</strong>
+    <ul>
+    	<li>当前订阅有效：最近一次事件是升级到高级（未取消）</li>
+    	<li>有降级记录：历史上没有降级</li>
+    	<li>结果：<strong>无风险客户</strong>（没有降级历史）</li>
+    </ul>
+    </li>
+    <li><strong>用户 504：</strong>
+    <ul>
+    	<li>当前订阅有效：最近一次事件是取消</li>
+    	<li>结果：<strong>无风险客户</strong>（已取消订阅）</li>
+    </ul>
+    </li>
+    <li><strong>用户 505：</strong>
+    <ul>
+    	<li>当前订阅有效：最近一次事件是升级到标准（未取消）</li>
+    	<li>有降级记录：历史上没有降级</li>
+    	<li>结果：<strong>无风险客户</strong>（没有降级历史）</li>
+    </ul>
+    </li>
+    <li><strong>用户 506：</strong>
+    <ul>
+    	<li>当前订阅有效：最近一次事件是降级到标准（未取消）</li>
+    	<li>有降级记录：是，历史上有 1 次降级</li>
+    	<li>当前订阅（9.99）vs 最大订阅（29.99）：9.99/29.99 = 33.3%（少于 50%）</li>
+    	<li>订阅天数：1 月&nbsp;20 日到 5 月 10 日 = 50 天（少于 60 天）</li>
+    	<li>结果：<strong>无风险客户</strong>（订阅时长不足）</li>
+    </ul>
+    </li>
+
+</ul>
+
+<p>结果表按 days_as_subscriber 降序排序，然后按&nbsp;user_id 升序排序。</p>
+
+<p><strong>注意：</strong>days_as_subscriber 按照每个用户的第一个事件日期到最后一个事件日期进行计算。</p>
+</div>
+
+<!-- description:end -->
+
+## 解法
+
+<!-- solution:start -->
+
+### 方法一
+
+<!-- tabs:start -->
+
+#### MySQL
+
+```sql
+
+```
+
+<!-- tabs:end -->
+
+<!-- solution:end -->
+
+<!-- problem:end -->