Valid Palindrome

package cn.edu.xidian.sselab.string;

import java.awt.datatransfer.StringSelection;

/**
*
* @author zhiyong wang
* title: Valid Palindrome
* content:
* 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.
*
*/
public class ValidPalindrome {

//这个题很多地方一开始没有想到，调试出了许多错误：
//1.没有注意到字符串里面有很多不是字母或者数字，如果是不是字母或者数字，要跳过他们，不管他们
//2.内部两个循环，第一落下了start小于end的约束条件，第二忘记把if改成while循环
//3.比较的时候忘记了还有大小写的情况，数字、字母都可以调用toLowerCase
public boolean isPalindrome(String s){
if(s == null) return false;
int len = s.length();
if(s.isEmpty()) return true;
int start = 0;
int end = len - 1;
while(start < end){
while(start < end && !Character.isLetterOrDigit(s.charAt(start)))
start++;
while(start < end && !Character.isLetterOrDigit(s.charAt(end)))
end--;
if(start < end && Character.toLowerCase(s.charAt(start)) != Character.toLowerCase(s.charAt(end)))
return false;
start++;
end--;
}
return true;
}
}