---
# System prepended metadata

title: '#17 Letter Combinations of a Phone Number'
tags: [LeetCode, ' Top100']

---

---
title: "#17 Letter Combinations of a Phone Number"
tags: LeetCode, Top100
---
#17 Letter Combinations of a Phone Number
==

題目描述
--
Given a string containing digits from ==2-9== inclusive, return all possible letter combinations that the number could represent. Return the answer in **any order**.

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

![](https://i.imgur.com/8aLC1ZE.png)

Example 1:
--
>Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]

解題思維
--
直接用簡單的歷程跑一遍。


Brute Force
--
```python=
class Solution:
    def letterCombinations(self, digits: str) -> List[str]:
        phone = {'2': ['a', 'b', 'c'],
                 '3': ['d', 'e', 'f'],
                 '4': ['g', 'h', 'i'],
                 '5': ['j', 'k', 'l'],
                 '6': ['m', 'n', 'o'],
                 '7': ['p', 'q', 'r', 's'],
                 '8': ['t', 'u', 'v'],
                 '9': ['w', 'x', 'y', 'z']}
        res = ['']
        if digits == '':
            return []
        for digit in digits:
            nows = res.copy()
            res = []
            for now in nows:
                for letter in phone[digit]:
                    res.append(now+letter)

        return res

```