LeetCode Valid Palindrome

1.题目

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.

2.解答

首先是题目的意思是：判断一个句子，正的读和倒着读是否都一样。比如"abba",就是正读和倒读都一样。这题只是多少忽略大小写，忽略非字母和数