LeetCode--125--验证回文串

问题描述：

好

times out:

 class Solution(object):
     def isPalindrome(self, s):
         """
         :type s: str
         :rtype: bool
         """
         j = len(s) - 1
         i = 0
         flag = True
         while i != j and flag == True:
             if s[i].isalnum() and s[j].isalnum():
                 if s[i].lower() == s[j].lower():
                     flag = True
                 else:
                     flag = False
             if not s[i].isalnum() :
                 i += 1
             if not s[j].isalnum():
                 j -= 1
         return flag
             

错误原因：相等的时候没有移动到下一个位置

 class Solution(object):
     def isPalindrome(self, s):
         """
         :type s: str
         :rtype: bool
         """
         j = len(s) - 1
         i = 0
         flag = True
         while i < j :
             if not s[i].isalnum() :
                 i += 1
                 continue
             if not s[j].isalnum():
                 j -= 1
                 continue
             if s[i].lower() != s[j].lower():
                     return False
             i += 1
             j -= 1
         return flag

官方：

 class Solution(object):
     def isPalindrome(self, s):
         """
         :type s: str
         :rtype: bool
         """
         new_s = "".join([i for i in s if i.isalnum() or i.isalpha()]).lower()
         return new_s == new_s[::-1]

正则表达式替换：

 class Solution(object):
     def isPalindrome(self, s):
         """
         :type s: str
         :rtype: bool
         """
         import re
         s = re.sub('[^a-z0-9]','',s.lower())
         return s == s[::-1]

正则复习请看：http://www.runoob.com/python/python-reg-expressions.html

视频：https://www.bilibili.com/video/av7036891?from=search&seid=10436462392778970383

2018-09-12 19:51:17