Valid Number

Problem

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 '.'.

Solution Approach

Expected Time Complexity: $O(n)$

Click - to see solution code

Python

class Solution:
    def isNumber(self, s: str) -> bool:
        states = [{},
                  {"blank": 1, "digit": 3, "sign": 2, ".": 4},
                  {"digit": 3, ".": 4},
                  {"digit": 3, "blank": 9, "e": 6, "E": 6, ".": 5},
                  {"digit": 5},
                  {"E": 6, "e": 6, "digit": 5, "blank": 9},
                  {"sign": 7, "digit": 8},
                  {"digit": 8},
                  {"digit": 8, "blank": 9},
                  {"blank": 9}]
        currentState = 1

        for i in s:
            c = i
            if i == ' ':
                c = "blank"
            elif i in ['+', '-']:
                c = "sign"
            elif i >= "0" and i <= '9':
                c = "digit"

            if c not in states[currentState].keys():
                return False

            currentState = states[currentState][c]

        if currentState not in [3, 5, 8, 9]:
            return False

        return True