[Leetcode] Valid Number

Problem

Validate if a given string is numeric. Some examples:

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

Algorithm

A valid number can contain, 0 ~ 9, at most one sign "+" or "-", at most one "." and at most "e" or "E". 

Some rules

• No "." after e
• "." must be adjacent to at least one number