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