Valid Number @python

Valid Number

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

直接上代码，特别是解法二，引入 re 模块匹配，很精简强大！

 class InputType:
     INVALID = 0
     SPACE = 1
     SIGN =2
     DIGIT =3
     DOT = 4
     EXPONENT =5

 class Solution:
     # @param s, a string
     # @return a boolean
     def isNumber(self, s):
         transition_table = [[-1,  0,  3,  1,  2, -1],     # next states for state 0
                             [-1,  8, -1,  1,  4,  5],     # next states for state 1
                             [-1, -1, -1,  4, -1, -1],     # next states for state 2
                             [-1, -1, -1,  1,  2, -1],     # next states for state 3
                             [-1,  8, -1,  4, -1,  5],     # next states for state 4
                             [-1, -1,  6,  7, -1, -1],     # next states for state 5
                             [-1, -1, -1,  7, -1, -1],     # next states for state 6
                             [-1,  8, -1,  7, -1, -1],     # next states for state 7
                             [-1,  8, -1, -1, -1, -1]]     # next states for state 8

         state = 0
         for char in s:
             inputType = InputType.INVALID
             if char.isspace():
                 inputType = InputType.SPACE;
             elif char == '+' or char == '-':
                 inputType = InputType.SIGN
             elif char in '':
                 inputType =InputType.DIGIT
             elif char  == '.':
                     inputType = InputType.DOT
             elif char == 'e' or char =='E':
                 inputType = InputType.EXPONENT

             state = transition_table[state][inputType]
             if state == -1:
                 return False
         return state==1 or state==4 or state ==7 or state==8

     def isNumber2(self,s):
         import re
         return bool(re.match("^\s*[\+\-]?((\d+(\.\d*)?)|\.\d+)([eE][+-]?\d+)?\s*$",s))