---
title: 【LeetCode】0065. Valid Number
date: 2019-01-04
is_modified: false
disqus: cynthiahackmd
categories:
- "面試刷題"
tags:
- "LeetCode"
---

{%hackmd @CynthiaChuang/Github-Page-Theme %}
<br>

Validate if a given string can be interpreted as a decimal number.

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Some examples:

"0"  =>  True  
" 0.1 "  =>  True  
"abc"  =>  False  
"1 a"  =>  False  
"2e10"  =>  True  
" -90e3 "  =>  True  
" 1e"  =>  False  
"e3"  =>  False  
" 6e-1"  =>  True  
" 99e2.5 "  =>  False  
"53.5e93"  =>  True  
" --6 "  =>  False  
"-+3"  =>  False  
"95a54e53"  =>  False

<br><br>

> **Note:** It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:
>
> - Numbers 0-9
> - Exponent - "e"
> - Positive/negative sign - "+"/"-"
> - Decimal point - "."
>
> Of course, the context of these characters also matters in the input.

<br>

**Related Topics:** `String`、`Math`

## 解題邏輯與實作
這題是要判斷給定的字串是否為一個合法的十進位數字，合法的數字中包含正負號、小數、科學記號 e，另外科學表示的部份 e 與後面的數字間可夾正號，最後是字串前後的的空白不影響判定。

基本上判定規則就這些，但需要特別注意兩個 case：`".1"` 與 `"3."` ，這兩種表示法也是合法的。

### 正規表示式 Regular Expression
這種抽 pattern 的問題，我第一個想到的是 Regular Expression，思考會比簡單，程式碼也簡潔許多。

import re

class Solution:
   def isNumber(self, s):
      reg = re.compile(r'^\s*[-+]?(\d+\.?|\.\d+)\d*(e[-+]?\d+)?\s*$')
      return re.match(reg, s) != None

## 其他連結
1. [【LeetCode】0000. 解題目錄](/x62skqpKStKMxRepJ6iqQQ)

<br><br>

> **本文作者**： 辛西亞．Cynthia
> **本文連結**： [辛西亞的技能樹](https://cynthiachuang.github.io/LeetCode-0065-Valid-Number) / [hackmd 版本](https://hackmd.io/@CynthiaChuang/LeetCode-0065-Valid-Number)
> **版權聲明**： 部落格中所有文章，均採用 [姓名標示-非商業性-相同方式分享 4.0 國際](https://creativecommons.org/licenses/by-nc-sa/4.0/deed.en) (CC BY-NC-SA 4.0) 許可協議。轉載請標明作者、連結與出處！