Determine Whether a String Is a Valid Number

Problem Statement

Given an ASCII string s, determine if it represents a valid number according to the following strict grammar rules:

1. No Whitespace: Leading, trailing, or embedded whitespace characters are not allowed.
2. Number Form: A valid number must be either a valid integer or a valid decimal, optionally followed by an exponent component.
3. Integer: An optional sign ('+' or '-'), followed by one or more digits (0-9).
4. Decimal: An optional sign ('+' or '-'), followed by one of the following patterns:
   • One or more digits followed by a dot . (e.g., "2.")
   • One or more digits followed by a dot . followed by one or more digits (e.g., "0.45")
   • A dot . followed by one or more digits (e.g., ".8") (Note: A standalone dot "." or "+." is invalid; at least one digit must be present).
5. Exponent: An 'e' or 'E' character followed by a valid integer (an optional sign '+' or '-' followed by one or more digits). Exponents cannot contain decimal points or additional exponents.
6. Unsupported Forms: Hexadecimal (0x...), binary (0b...), octal, commas, and other notations are strictly invalid.

Return True if s is a valid number, and False otherwise.

Function Signature

def is_valid_number(s: str) -> bool:
    pass

Constraints

• 1 <= len(s) <= 100
• s consists of English letters, digits (0-9), '+', '-', '.', and whitespace characters.

Examples

Example 1

Input: s = "-0.1e+5"
Output: True
Explanation: The base is a valid decimal "-0.1", followed by an exponent 'e' with a signed integer "+5".

Example 2

Input: s = "1e2.5"
Output: False
Explanation: The exponent part must be an integer, but "2.5" contains a decimal point.

Example 3

Input: s = " .1 "
Output: False
Explanation: Whitespace is not permitted.

Edge Cases to Consider

• Dot without digits before or after: ".", "+." (Invalid)
• Missing digits around exponent: "e", "1e", "e3" (Invalid)
• Multiple signs or misplaced signs: "++1", "1+" (Invalid)
• Multiple dots or dots in exponent: "1.2.3", "1e2.0" (Invalid)