166. validate number string

Give a number string, check if it is valid number.

By "valid", we mean if it validates as one of below formats:

1. integer, such as '0', '-1'
2. decimal number like '1.0', '-2.335'
3. exponential notation -12.3e45

Formats such as BigInt, Infinity, NaN, octal and hexadecimal .etc are out of scope, you can treat them as invalid.

Pay attention to the sign + -.

Note

The test cases are not covering all the possible cases, since this is not a problem to test your knowledge against JavaScript language spec.

You should confirm with your interviewer about the scope and those edge cases.

isNaN() seems to be a nice trick, but could you solve without it?