【leetcode】Valid Palindrome

题目简述：

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：

class Solution:

    # @param s, a string

    # @return a boolean

    def isPalindrome(self, s):

        if s == '':

            return True

        s = s.strip().lower()

        t = ''

        for i in s:

            if (i <= '9' and i >= '0') or (i <= 'z' and i >= 'a'):

                t += i

        l = len(t)

        for i in range(l/2):

            if t[i] != t[l-i-1]:

                return False

        return True