题解 | #表示数值的字符串#

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param str string字符串 
# @return bool布尔型
#
class Solution:
    def isNumeric(self , str: str) -> bool:
        # write code here
        n = len(str)
        index = 0
        has_num = has_sign = has_e = has_dot = False

        while index<n and str[index] == ' ':
            index += 1
        while index<n:
            while index<n and '0'<=str[index]<='9':
                index += 1
                has_num = True
            if index == n:
                break
            if str[index] == 'e' or str[index] == 'E':
                if has_e or not has_num:
                    return False
                has_e = True
                has_num = has_sign = has_dot = False
            elif str[index]=='+' or str[index]=='-':
                if has_sign or has_num or has_dot:
                    return False
                has_sign = True
            elif str[index] == '.':
                if has_dot or has_e:
                    return False
                has_dot = True
            elif str[index] == ' ':
                break
            else:
                return False
            index += 1
        while index <n and str[index]==' ':
            index += 1
        return has_num and index == n