How should I practice Valid Number with Exponents?

Start by reading the full statement, solve the visible examples, then compare the pattern against related LinkedIn phone screen problems in FastPrep.

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Valid Number with Exponents

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Problem statement

Given a string s, return true if the entire string represents a valid number under the following grammar, or false otherwise. Validate the spelling; do not convert it to a numeric type.

The mantissa may begin with one optional + or - sign.
After that sign, the mantissa is either one or more digits with an optional decimal point and zero or more following digits, or a decimal point followed by one or more digits.
The mantissa may be followed by one exponent: e or E, an optional + or - sign, and one or more digits. Decimal points are not allowed in the exponent.
Digits are the ASCII characters 0 through 9. No whitespace or other characters are allowed in a valid number.

For example, 7, -7., +.5, and 7e-2 are valid. The empty string, ., and 7e are invalid. Leading zeros and arbitrarily large magnitudes are allowed within the input length limit.

Function

isNumber(s: String) → boolean

Examples

Example 1

s = "-12.5e+2"return = true

The mantissa -12.5 has an optional minus sign and digits on both sides of its decimal point. The exponent e+2 has a marker, an optional plus sign, and a digit. The whole string follows the grammar.

Example 2

s = ".4"return = true

A mantissa may start with a decimal point when at least one digit follows it. The digit 4 satisfies that requirement, and an exponent is optional.

Example 3

s = "4e+"return = false

The mantissa 4 is valid, but the exponent has a marker and a sign with no digit after them.

Constraints

0 <= s.length <= 10000.
Each character in the input is printable ASCII, with a code from 32 through 126.
Inputs need not be valid numbers; return false for any spelling outside the grammar.