剑指Offer(Python多种思路实现):表示数值的字符串

剑指Offer(Python多种思路实现):表示数值的字符串

面试20题：

题目：表示数值的字符串

题：请实现一个函数用来判断字符串是否表示数值（包括整数和小数）。例如，字符串"+100","5e2","-123","3.1416"和"-1E-16"都表示数值。 但是"12e","1a3.14","1.2.3","+-5"和"12e+4.3"都不是。

解题思路一：

class Solution:
    def isNumeric(self, s):
        # write code here
        try:
            return float(s)
        except:
            return 0

解题思路二：

class Solution:
     def isNumeric(self, s):
        # write code here
        if not s or len(s)<=0:
            return False
        alist=[i.lower() for i in s]
        if 'e' in alist:
            index=alist.index('e')
            front=alist[:index]
            behind=alist[index+1:]
            if '.' in behind or len(behind)==0:
                return False
            isfront=self.isDigit(front)
            isbehind=self.isDigit(behind)
            return isfront and isbehind
        else:
            return self.isDigit(alist)
        
    def isDigit(self,alist):
        dotNum=0
        allow_num = ['0', '1', '2', '3', '4', '5',
                     '6', '7', '8', '9', '+', '-', '.']
        for i in range(len(alist)):
            if alist[i] not in allow_num:
                return False
            if alist[i]=='.':
                dotNum += 1
            if alist[i] in '+-' and i!=0:
                return False
        if dotNum>1:
            return False
        return True