Sword finger offer (53): a string representing a numeric value

solution 1： There may be a positive or negative ’+‘ perhaps ’-’. Next are several 0 To 9 The digits of represent the integer part of the value （ In some decimals, there may be no integer part of the value ）. If the number is a decimal , Then there may be several after the decimal 0 To 9 The digits of represent the decimal part of the value . If the numerical value is expressed in scientific notation , Next is a ’e’ perhaps ’E’, And an integer immediately following （ It can have a plus or minus sign ） The index .
When judging whether a string conforms to the above pattern , First, check whether the first character is a sign . If it is , Move a character on the string , Continue scanning the remaining strings 0 To 9 The number of . If it is a decimal , You will encounter a decimal point . in addition , If it is a numerical value expressed by scientific notation , After integers or decimals, you may encounter ’e’ perhaps ’E’.

 class Solution:
    # s character string 
    def isNumeric(self, s):
        # write code here
        if len(s) <= 0:
            return False
        has_sign = False
        has_point = False
        has_e = False
        for i in range(len(s)):
            if s[i] == 'E' or s[i] == 'e':
                if has_e:
                    return False
                else:
                    has_e = True
                    if i == len(s) - 1:
                        return False
            elif s[i] == '+' or s[i] == '-':
                if has_sign:
                    if s[i-1] != 'e' and s[i-1] !='E':
                        return False
                else:
                    has_sign = True
                    if i > 0 and s[i-1] != 'e' and s[i-1] != 'E':
                        return False
            elif s[i] == '.':
                if has_point or has_e:
                    return False
                else:
                    has_point = True
                    if i >0 and (s[i-1] == 'e' or s[i-1] == 'E'):
                        return False
            else:
                if s[i] < '0' or s[i] >'9':
                    return False
        return True