# 字母大小写全排列

<p>给定一个字符串<code>S</code>，通过将字符串<code>S</code>中的每个字母转变大小写，我们可以获得一个新的字符串。返回所有可能得到的字符串集合。</p>

<p>&nbsp;</p>

<pre><strong>示例：</strong>
<strong>输入：</strong>S = &quot;a1b2&quot;
<strong>输出：</strong>[&quot;a1b2&quot;, &quot;a1B2&quot;, &quot;A1b2&quot;, &quot;A1B2&quot;]

<strong>输入：</strong>S = &quot;3z4&quot;
<strong>输出：</strong>[&quot;3z4&quot;, &quot;3Z4&quot;]

<strong>输入：</strong>S = &quot;12345&quot;
<strong>输出：</strong>[&quot;12345&quot;]
</pre>

<p>&nbsp;</p>

<p><strong>提示：</strong></p>

<ul>
	<li><code>S</code>&nbsp;的长度不超过<code>12</code>。</li>
	<li><code>S</code>&nbsp;仅由数字和字母组成。</li>
</ul>

<p>以下错误的选项是？</p>

## aop

### before

```cpp

```
### after

```cpp

```

## 答案

```cpp

```

## 选项


### A

```cpp

```

### B

```cpp

```

### C

```cpp

```
