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 '0123456789':
                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))