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.

 

 to see which companies asked this question

 

1 public class Solution { 2     public boolean isPalindrome(String s) { 3         if(s.trim() == "") return true; 4         int i = 0,j = s.length()-1; 5         char c1,c2; 6         while(i <= j){ 7             c1 = s.charAt(i); 8             c2 = s.charAt(j); 9             if(!Character.isLetterOrDigit(c1)) i++;10             if(!Character.isLetterOrDigit(c2)) j--;11             if(Character.isLetterOrDigit(c1) && Character.isLetterOrDigit(c2)){12                 if(Character.toLowerCase(c1) != Character.toLowerCase(c2)) return false;13                 i++;14                 j--;15             }16         }17         return true;18     }19 }

主要是注意该题中 , . ! 等等不算在回文的序列中。