Coming up with edge cases

## PROBLEM

https://leetcode.com/problems/valid-number/

A valid number can be split up into these components (in order):

- A decimal number or an integer.
- (Optional) An 'e' or 'E', followed by an integer.

A decimal number can be split up into these components (in order):

- (Optional) A sign character (either '+' or '-').
- One of the following formats:
- One or more digits, followed by a dot '.'.
- One or more digits, followed by a dot '.', followed by one or more digits.
- A dot '.', followed by one or more digits.

An integer can be split up into these components (in order):

- (Optional) A sign character (either '+' or '-').
- 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.

Constraints:
- 1 <= s.length <= 20
- s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.














## SOLUTION

Let's come up with edge cases for these two cases separately, starting with the simpler one (integers):

### Integers
- Let's first consider edge cases without the sign characters.
  - Let's consider length as a source of edge cases:
    - '' is invalid
  - Anything with 'a', '1a',
-