LeetCode--125--验证回文串

问题描述：

好

times out:

 1 class Solution(object):
 2     def isPalindrome(self, s):
 3         """
 4         :type s: str
 5         :rtype: bool
 6         """
 7         j = len(s) - 1
 8         i = 0
 9         flag = True
10         while i != j and flag == True:            
11             if s[i].isalnum() and s[j].isalnum():
12                 if s[i].lower() == s[j].lower():
13                     flag = True       
14                 else:
15                     flag = False
16             if not s[i].isalnum() :
17                 i += 1
18             if not s[j].isalnum():
19                 j -= 1
20         return flag
21             

错误原因：相等的时候没有移动到下一个位置

 1 class Solution(object):
 2     def isPalindrome(self, s):
 3         """
 4         :type s: str
 5         :rtype: bool
 6         """
 7         j = len(s) - 1
 8         i = 0
 9         flag = True
10         while i < j :            
11             if not s[i].isalnum() :
12                 i += 1
13                 continue
14             if not s[j].isalnum():  
15                 j -= 1
16                 continue
17             if s[i].lower() != s[j].lower():    
18                     return False
19             i += 1
20             j -= 1
21         return flag

官方：

1 class Solution(object):
2     def isPalindrome(self, s):
3         """
4         :type s: str
5         :rtype: bool
6         """
7         new_s = "".join([i for i in s if i.isalnum() or i.isalpha()]).lower()
8         return new_s == new_s[::-1]

正则表达式替换：

1 class Solution(object):
2     def isPalindrome(self, s):
3         """
4         :type s: str
5         :rtype: bool
6         """
7         import re
8         s = re.sub('[^a-z0-9]','',s.lower())
9         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