125. Valid Palindrome

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

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

Example 1:

1 2	Input: "A man, a plan, a canal: Panama" Output: true

Example 2:

1 2	Input: "race a car" Output: false

判斷是不是回文，把字串去掉大小寫跟符號，比對反轉是否相同就可以了。

T: O(1), S: O(1)
class Solution:
    def isPalindrome(self, s: str) -> bool:
        s = s.lower();
        s = re.sub('[^a-z0-9]','',s) # clear everything except a-z, 0-9
        print(s)
        if s == s[::-1]: 
            return True
        else:
            return False

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