Given a string s, return whether s is a valid number.
For example, all the following are valid numbers: "2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789", while the following are not valid numbers: "abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53".
Formally, a valid number is defined using one of the following definitions:
An integer number is defined with an optional sign '-' or '+' followed by digits.
A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions:
An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number.
The digits are defined as one or more digits.
Examples
Example 1
Input: s = "0"
Output: true
Example 2
Input: s = "e"
Output: false
Example 3
Input: s = "."
Output: false
Constraints
1 <= s.length <= 20
s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.
65. Valid Number
Hard
50 Points
String
Given a string s, return whether s is a valid number.
For example, all the following are valid numbers: "2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789", while the following are not valid numbers: "abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53".
Formally, a valid number is defined using one of the following definitions:
An integer number is defined with an optional sign '-' or '+' followed by digits.
A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions:
An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number.
The digits are defined as one or more digits.
Examples
Example 1
Input: s = "0"
Output: true
Example 2
Input: s = "e"
Output: false
Example 3
Input: s = "."
Output: false
Constraints
1 <= s.length <= 20
s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.