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Leetcode[125] Valid Palindrome

09 Nov 2015

###Task1 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.

###Python ####Complex

import re
class Solution(object):
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if not s:
            return True
        s = re.sub("[^a-zA-Z0-9]", "", s).lower()
        if len(s) == 0:
            return True
        mid = len(s) / 2
        for i in range(mid + 1):
            if s[i] != s[-1 - i]:
                return False
        return True

####Simple

import re
class Solution(object):
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if not s:
            return True
        if len(s) == 0:
            return True
        start = 0
        end = len(s) - 1
        while start < end:
            while start < end and not s[start].isalnum():
                start += 1
            while start < end and not s[end].isalnum():
                end -= 1
            if s[start].lower() != s[end].lower():
                return False
            start += 1
            end -= 1
        return True

###Java

public class Solution {
    public boolean isPalindrome(String s) {
        if (s == null) {
            return false;
        }
        if (s.length() == 0) {
            return true;
        }
        
        s = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
        int start = 0;
        int end = s.length() - 1;
        while (start < end) {
            if (s.charAt(start) != s.charAt(end)) {
                return false;
            }
            start++;
            end--;
        }
        
        return true;
    }
}

###Points

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