LeetCode 65 ValidNumer(Python详解及实现)

【题目】

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 problemstatement to be ambiguous. You should gather all requirements up front beforeimplementing one.

　输入一个字符串，判断这个字符串表示的是不是一个有效的数字。比如：

　　"0" => true

　　"  0.1 " => true

　　"abc" => false

　　"1  a" => false

　　"2e10" => true

【思路】

这个题目难点在于考虑要全面，空格在字符串两端不影响;在字符串中间出现为false;正负号在第一个出现的数字前出现为True;正负号在E或e之后出现且后面有数字的为true;E或e出现在数字中间，两边均为数字才合理。

【Python实现】

class Solution(object):

   def isNumber(self, s):

       """

       :type s: str

       :rtype: bool

       """

       begin, last = 0, len(s) - 1

       while begin <= last and s[begin] == ' ':#若起始为空格，下移一位判断

           begin += 1

       while begin <= last and s[last] == ' ':#若末尾为空格，上移一位判断

           last -= 1

       '''if begin < last and (s[begin] == '+' or s[begin] == '-'):#如果当前位为正号或符号，下移一位检测下一位是否为数字

           begin += 1'''

       num, dot, exp = False, False, False#数字，点，exp标志位

       start = begin#记录下最开始不是空格的位置

       while begin <= last:

           if s[begin] >= '0' and s[begin] <= '9':#检测当前位是否为数字

                num = True

           elif s[begin] == '.' :

                #if begin != last:

                    #return False

                if dot or exp:

                    print(1)

                    return False

                dot = True

           elif s[begin] == 'e' or s[begin] == 'E':

                if exp or not num:

                    print(2)

                    return False

                exp,num = True,False

           elif s[begin] == '+' or s[begin] == '-':

                 if begin != start and s[begin- 1] != 'e':

#首个是符号，或者当前字符为符号时候若前一个字符不是e，直接返回          

                     return False

           else:

                print(4)

                return False

           begin += 1

       print(5)

       return num

   

if __name__ == '__main__':

    S= Solution()

    s= ' -54.53061'

   S.isNumber(s)