Practice/Meta/Leetcode 65. Valid Number

Leetcode 65. Valid Number

CodingMust

Problem

Write a function that validates whether a given string represents a properly formatted numeric value. The string should match the structure of a valid number according to these rules:

A valid number consists of an optional sign character (+ or -), followed by a numeric body, and optionally an exponent part.

The numeric body can be:

• An integer (one or more digits)

• A decimal number (digits with a decimal point)

  • Format: digits.digits (e.g., "123.456")
  • Format: digits. (e.g., "123.")
  • Format: .digits (e.g., ".456")

The exponent part (if present) consists of:

• The letter e or E
• An optional sign (+ or -)
• One or more digits

Your function should return true if the string is a valid number, and false otherwise.

Requirements

1. The function must handle all combinations of sign, decimal notation, and exponent notation
2. A lone decimal point (just ".") without any digits is invalid
3. The exponent part must have at least one digit after the e or E
4. At least one digit must be present in the numeric body (before the exponent)
5. No whitespace or other characters are allowed
6. Empty strings are invalid

Constraints

• 1 ≤ s.length ≤ 100
• s consists only of English letters, digits, plus +, minus -, and dot .
• You may assume the input contains only ASCII characters

Examples

Example 1:

Input: s = "42" Output: true Explanation: A straightforward positive integer.

Example 2:

Input: s = "-0.75" Output: true Explanation: A negative decimal number with both integer and fractional parts.

Example 3:

Input: s = "6e-1" Output: true Explanation: Integer with negative exponent (represents 0.6).

Example 4:

Input: s = "." Output: false Explanation: Just a decimal point with no digits is not a valid number.

Example 5:

Input: s = "99e2.5" Output: false Explanation: The exponent part cannot contain a decimal point.

Example 6:

Input: s = ".8" Output: true Explanation: Decimal without integer part is valid if fractional part exists.