LeetCode Hard — Valid Number

A valid number can be split up into these components (in order):

1. A decimal number or an integer.
2. (Optional) An 'e' or 'E', followed by an integer.

A decimal number can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. One of the following formats:
   1. One or more digits, followed by a dot '.'.
   2. One or more digits, followed by a dot '.', followed by one or more digits.
   3. A dot '.', followed by one or more digits.

An integer can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. One or more digits.

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"].

Given a string s, return true if s is a valid number.

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 '.'.

Java Solution

You can use regular expressions to validate whether a given string is a valid number or not. Here’s a Java solution using regular expressions:

import java.util.regex.Pattern;

public class ValidNumber {
    public static boolean isNumber(String s) {
        // Define the regular expression pattern for a valid number
        String regex = "^[+-]?((\\d+(\\.\\d*)?)|(\\.\\d+))(e[+-]?\\d+)?$";
        return Pattern.matches(regex, s);
    }

    public static void main(String[] args) {
        System.out.println(isNumber("0"));      // Output: true
        System.out.println(isNumber("e"));      // Output: false
        System.out.println(isNumber("."));      // Output: false
        System.out.println(isNumber("2e10"));   // Output: true
        System.out.println(isNumber("abc"));    // Output: false
    }
}

This Java code defines a regular expression pattern regex to match valid numbers according to the given criteria. The isNumber method uses the Pattern.matches method to check if the input string matches the pattern. The provided test cases demonstrate its usage.

Python Solution

import re

def isNumber(s):
    # Define the regular expression pattern for a valid number
    pattern = re.compile(r'^[+-]?((\d+(\.\d*)?)|(\.\d+))(e[+-]?\d+)?$')
    return bool(pattern.match(s))

# Test cases
print(isNumber("0"))      # Output: True
print(isNumber("e"))      # Output: False
print(isNumber("."))      # Output: False
print(isNumber("2e10"))   # Output: True
print(isNumber("abc"))    # Output: False

This Python code uses the re module to define a regular expression pattern pattern. The re.compile function is used to compile the regular expression, and the match method is then used to check if the input string matches the pattern. The provided test cases demonstrate its usage.