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:
Are you consider that the string might is empty? This was a good question to ask during a interview.

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

solution 1:using Regular expression.

1 defIspalindrome (self, s):2P=re.compile ('\w')3Arr=P.findall (s)4N=len (arr)/25          forIinchrange (n):6             ifArr[i].upper ()!=arr[n-1-i].upper ():7                 returnFalse8         returnTrue

Solution 2: A simpler of the using regular expression.

1 def Ispalindrome (self, s): 2         s = re.sub ("[^a-za-z0-9]"""", s). Lower ()  # can be replaced by ' \w '3         return s = = S[::-1]

Solution 3:just traverse the string.

1 def Ispalindrome (s): 2         "'  for inch if Ch.isalnum ()). Lower ()3         return S1 = = S1[::-1]

leetcode#125 Valid palindrome