Q125 Valid Palindrome

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.

解题思路：

参考题目 Q9 Palindrome Number

只包含字母或数字的回文数，因此先全部转化为小写，然后过滤掉其他非字母或非数字字符，然后反转比较。

Python实现：

class Solution:
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        s = s.lower() # 先将字符串转化为全小写
        filtStr = ''
        for ch in s:  # 过滤掉非字母和非数字字符
            if 'a' <= ch <= 'z' or '0' <= ch <= '9':
                filtStr += ch
        if filtStr == filtStr[::-1]:
            return True
        else:
            return False

a = 'aBc 122-1c, b:A'
b = Solution()
print(b.isPalindrome(a))  # True