# [17. Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)


## 题目

Given a string containing digits from `2-9` inclusive, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Telephone-keypad2.svg/200px-Telephone-keypad2.svg.png)

**Example:**

```c
Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
```

**Note:**

Although the above answer is in lexicographical order, your answer could be in any order you want.

## 题目大意

给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。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。


## 解题思路

- DFS 递归深搜即可