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Kotlin-based LeetCode algorithm problem solutions, regularly updated
65\. Valid Number
Hard
A **valid number** can be split up into these components (in order):
1. A **decimal number** or an **integer**.
2. (Optional) An `'e'` or `'E'`, followed by an **integer**.
A **decimal number** can be split up into these components (in order):
1. (Optional) A sign character (either `'+'` or `'-'`).
2. One of the following formats:
1. One or more digits, followed by a dot `'.'`.
2. One or more digits, followed by a dot `'.'`, followed by one or more digits.
3. A dot `'.'`, followed by one or more digits.
An **integer** can be split up into these components (in order):
1. (Optional) A sign character (either `'+'` or `'-'`).
2. One or more digits.
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"]`.
Given a string `s`, return `true` _if_ `s` _is a **valid number**_.
**Example 1:**
**Input:** s = "0"
**Output:** true
**Example 2:**
**Input:** s = "e"
**Output:** false
**Example 3:**
**Input:** s = "."
**Output:** false
**Constraints:**
* `1 <= s.length <= 20`
* `s` consists of only English letters (both uppercase and lowercase), digits (`0-9`), plus `'+'`, minus `'-'`, or dot `'.'`.