<p>给定一个仅包含数字 <code>2-9</code> 的字符串，返回所有它能表示的字母组合。答案可以按 <strong>任意顺序</strong> 返回。</p>

<p>给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。</p>

<p><img src="https://assets.leetcode-cn.com/aliyun-lc-upload/original_images/17_telephone_keypad.png" style="width: 200px;" /></p>

<p> </p>

<p><strong>示例 1：</strong></p>

<pre>
<strong>输入：</strong>digits = "23"
<strong>输出：</strong>["ad","ae","af","bd","be","bf","cd","ce","cf"]
</pre>

<p><strong>示例 2：</strong></p>

<pre>
<strong>输入：</strong>digits = ""
<strong>输出：</strong>[]
</pre>

<p><strong>示例 3：</strong></p>

<pre>
<strong>输入：</strong>digits = "2"
<strong>输出：</strong>["a","b","c"]
</pre>

<p> </p>

<p><strong>提示：</strong></p>

<ul>
	<li><code>0 <= digits.length <= 4</code></li>
	<li><code>digits[i]</code> 是范围 <code>['2', '9']</code> 的一个数字。</li>
</ul>
<div><div>Related Topics</div><div><li>哈希表</li><li>字符串</li><li>回溯</li></div></div><br><div><li>👍 1453</li><li>👎 0</li></div>