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49 lines
1.9 KiB
Markdown
49 lines
1.9 KiB
Markdown
# [65. Valid Number](https://leetcode.com/problems/valid-number/)
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## 题目
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A **valid number** can be split up into these components (in order):
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1. A **decimal number** or an integer.
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2. (Optional) An 'e' or 'E', followed by an **integer.**
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A **decimal number** can be split up into these components (in order):
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1. (Optional) A sign character (either '+' or '-').
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2. One of the following formats:
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1. One or more digits, followed by a dot '.'.
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2. One or more digits, followed by a dot '.', followed by one or more digits.
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3. A dot '.', followed by one or more digits.
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An **integer** can be split up into these components (in order):
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1. (Optional) A sign character (either '+' or '-').
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2. One or more digits.
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For example, all the following are valid numbers: `["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"]`, while the following are not valid numbers: `["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].`
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Given a string s, return true if s is a **valid number.**
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**Example:**
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Input: s = "0"
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Output: true
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Input: s = "e"
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Output: false
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## 题目大意
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给定一个字符串S，请根据以上的规则判断该字符串是否是一个有效的数字字符串。
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## 解题思路
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- 用三个变量分别标记是否出现过数字、是否出现过'.'和 是否出现过 'e'
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- 从左到右依次遍历字符串中的每一个元素
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- 如果是数字，则标记数字出现过
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- 如果是 '.', 则需要 '.'没有出现过，并且 e 没有出现过，才会进行标记
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- 如果是 'e/E', 则需要 'e'没有出现过，并且前面出现过数字，才会进行标记
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- 如果是 '+/-', 则需要是第一个字符，或者前一个字符是 'e/E'，才会进行标记，并重置数字出现的标识
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- 最后需要字符串中至少出现过数字，避免下列case: s == '.' or 'e/E' or '+/e' and etc... |