Valid Number

Problem Statement

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

A decimal number or an integer. (Optional) An 'e' or 'E', followed by an integer. A decimal number can be split up into these components (in order):

(Optional) A sign character (either '+' or '-').

One of the following formats: One or more digits, followed by a dot '.'.

One or more digits, followed by a dot '.', followed by one or more digits. A dot '.', followed by one or more digits.

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

(Optional) A sign character (either '+' or '-'). 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.

Leetcode Link

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 '.'.

Code

Python Code

class Solution(object):
  def isNumber(self, s):
      """
      :type s: str
      :rtype: bool
      """
      #define a DFA
      state = [{},
              {'blank': 1, 'sign': 2, 'digit':3, '.':4},
              {'digit':3, '.':4},
              {'digit':3, '.':5, 'e':6, 'blank':9},
              {'digit':5},
              {'digit':5, 'e':6, 'blank':9},
              {'sign':7, 'digit':8},
              {'digit':8},
              {'digit':8, 'blank':9},
              {'blank':9}]
      currentState = 1
      for c in s:
          if c >= '0' and c <= '9':
              c = 'digit'
          if c == ' ':
              c = 'blank'
          if c in ['+', '-']:
              c = 'sign'
          if c not in state[currentState].keys():
              return False
          currentState = state[currentState][c]
      if currentState not in [3,5,8,9]:
          return False
      return True