leetcode125

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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:

Input: “A man, a plan, a canal: Panama”
Output: true
Example 2:

Input: “race a car”
Output:

Idea

the python string operations:
string1.join([….])
string2.lower()

Code

Mine

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class Solution(object):
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if not s:
            return True
        l, r = 0, len(s) - 1
        while l < r:
            while l < r and (not (s[l].isalpha() or s[l].isdigit())):
                l += 1
            while l < r and (not (s[r].isalpha() or s[r].isdigit())):
                r -= 1
            if s[l].lower() != s[r].lower():
                return False
            l += 1
            r -= 1
        return True

more concise

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class Solution(object):
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        s = ''.join([x for x in s if x.isalpha() or x.isdigit()]).lower()
        return s == s[::-1]