leetcode 面试题20 表示数值的字符串

解题思路：这个没有什么技巧，就是把所有的情况都考虑到就可以了

class Solution:
    def isNumber(self, s: str) -> bool:
        tabel = ['e', '.', '+', '-']
        s = s.strip()
        if len(s) > 0 and (s[0] == '+' or s[0] == '-'):
            s = s[1:]
        lens = len(s)
        if lens == 0:
            return False
        i = 0
        while(i < lens):
            if 0 <= (ord(s[i]) - ord('0')) <= 9:
                i += 1
                continue
            elif s[i] in tabel:
                if (s[i] == '+' or s[i] == '-') and 'e' in tabel:
                    return False
                elif s[i] == '.' :
                    if 'e' not in tabel or (i >= (lens-1) and i <= 0):
                        return False
                    tabel.remove('.')
                elif s[i] == 'e':
                    if i <= 0 or i >= (lens-1):
                        return False
                    if s[i+1] == '+' or s[i+1] == '-':
                        if i + 2 >= lens:
                            return False
                        i += 1
                    tabel.remove('+')
                    tabel.remove('-')
                    if s[i-1] == '.' and (i - 1) <= 0:
                        return False
                    tabel.remove('e')

                i += 1
            else:
                return False
        return True