LeetCode#125 Valid Palindrome

Problem Definition:

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.

 

Solution 1: Using regular expression.

def isPalindrome(self, s):
        p=re.compile('w')
        arr=p.findall(s)
        n=len(arr)/2
        for i in range(n):
            if arr[i].upper()!=arr[n-1-i].upper():
                return False
        return True

Solution 2: A simpler way of using regular expression.

def isPalindrome(self, s):
        s = re.sub("[^A-Za-z0-9]", "", s).lower()  #可以换成'W'
        return s == s[::-1]

Solution 3: Just traverse the string.

def isPalindrome(s):
        s1 = ''.join(ch for ch in s if ch.isalnum()).lower()
        return s1 == s1[::-1]