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leetcode-cn/problem (Chinese)/查找合法邮箱 [find-valid-emails].html Normal file
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<p>表：<code>Users</code></p>
<pre>
+-----------------+---------+
| Column Name | Type |
+-----------------+---------+
| user_id | int |
| email | varchar |
+-----------------+---------+
(user_id) 是这张表的唯一主键。
每一行包含用户的唯一 ID 和邮箱地址。
</pre>
<p>编写一个解决方案来查找所有 <b>合法邮箱地址</b>。一个合法的邮箱地址符合下述条件：</p>
<ul>
<li>只包含一个&nbsp;<code>@</code>&nbsp;符号。</li>
<li>以&nbsp;<code>.com</code>&nbsp;结尾。</li>
<li><code>@</code>&nbsp;符号前面的部分只包含&nbsp;<strong>字母数字</strong>&nbsp;字符和&nbsp;<strong>下划线</strong>。</li>
<li><code>@</code>&nbsp;符号后面与&nbsp;<code>.com</code>&nbsp;前面的部分 包含 <strong>只有字母&nbsp;</strong>的域名。</li>
</ul>
<p>返回结果表以&nbsp;<code>user_id</code> <strong>升序</strong>&nbsp;排序。</p>
<p>&nbsp;</p>
<p><strong class="example">示例：</strong></p>
<div class="example-block">
<p><strong>输入：</strong></p>
<p>Users 表：</p>
<pre class="example-io">
+---------+---------------------+
| user_id | email |
+---------+---------------------+
| 1 | alice@example.com |
| 2 | bob_at_example.com |
| 3 | charlie@example.net |
| 4 | david@domain.com |
| 5 | eve@invalid |
+---------+---------------------+
</pre>
<p><strong>输出：</strong></p>
<pre class="example-io">
+---------+-------------------+
| user_id | email |
+---------+-------------------+
| 1 | alice@example.com |
| 4 | david@domain.com |
+---------+-------------------+
</pre>
<p><strong>解释：</strong></p>
<ul>
<li><strong>alice@example.com</strong>&nbsp;是合法的因为它包含一个&nbsp;<code>@</code>，alice 是只有字母数字的，并且&nbsp;example.com 以字母开始并以 .com&nbsp;结束。</li>
<li><strong>bob_at_example.com</strong>&nbsp;是不合法的因为它包含下划线但没有&nbsp;<code>@</code>。</li>
<li><strong>charlie@example.net</strong>&nbsp;是不合法的因为域名没有以&nbsp;<code>.com</code>&nbsp;结尾。</li>
<li><strong>david@domain.com</strong>&nbsp;是合法的因为它满足所有条件。</li>
<li><strong>eve@invalid</strong>&nbsp;是不合法的因为域名没有以&nbsp;<code>.com</code>&nbsp;结尾。</li>
</ul>
<p>结果表以 user_id 升序排序。</p>
</div>