LeetCode | Valid Palindrome

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.

可以直接用java的正则匹配去除非字母数字的字符，并将字符串统一为大写或小写，然后首尾两两比较即可。

如果对于java提供的正则匹配性能不满意，可以自己实现，主要是两个细节：非字母数字的过滤、大小写转换。

代码

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

LeetCode | Valid Palindrome

原文：http://blog.csdn.net/perfect8886/article/details/19674843