问题描写叙述：

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.

代码：

import java.util.Vector;public class Valid_Palindrome {	public boolean isPalindrome(String s) {		s = s.toLowerCase();		Vector
     
       vector = new Vector
      
       ();        for(int i = 0; i< s.length(); i++){        	Character ch = s.charAt(i);        	if((ch >='a' && ch <='z' )||(ch >='0' && ch <='9'))        		vector.add(ch);        }                if(vector.size() == 0)        	return true;                int size = vector.size();        for(int i=0; i< size/2; i++){        	if(vector.get(i) != vector.get(size-1-i))        		return false;        }        return true;    }}