Longest Palindromic Substring

[xqian]

http://leetcode.com/onlinejudge#question_5
http://leetcode.com/2011/11/longest-palindromic-substring-part-i.html
http://leetcode.com/2011/11/longest-palindromic-substring-part-ii.html

And another little problem, that might worthy to take a look:
Valid Palindrome
http://leetcode.com/onlinejudge#question_125