【leetcode】125. Valid Palindrome【E】【92】

原创于 2016-07-05 19:48:09 发布 · 371 阅读

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本文介绍了一种使用Python正则表达式来过滤非字母数字字符并忽略大小写的方法，以确定给定字符串是否为回文。同时探讨了空字符串的情况。

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Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

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用最笨的办法，对字符串每个字符，挨个判断，是否是数字和字母

然后再大小写字母转换，不过超时了

那看来只能用正则表达式了

几行就搞定了

class Solution(object):
    def isPalindrome(self, s):
        res = re.sub(r'\W', "", s)
        res = res.lower()
        return res == res[::-1]

        # for i in s:
        #     # print ord('0')
        #     if ord(i) <= ord('z') and ord(i) >= ord('a'):
        #         res = res + i
        #     elif ord(i) <= ord('Z') and ord(i) >= ord('A'):
        #         res = res + chr(ord(i)+32)
        #     elif ord(i) >= ord('0') and ord(i) <= ord('9'):
        #         res =res + i
        # print res[::-1]
        # print res

        # return res == res[::-1]