Valid Palindrome（LintCode）

Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

 

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.

Challenge

O(n) time without extra memory.

深刻体会到了英文的用处。。。题目的中文翻译真是误导人。

 public class Solution {
     /**
      * @param s A string
      * @return Whether the string is a valid palindrome
      */
     public boolean isPalindrome(String s) {
         char[] cs = s.toCharArray();
         int i = 0;
         int j = cs.length - 1;

         while(i<j) {
             while(i<j && !Character.isDigit(cs[i]) && !Character.isLetter(cs[i])) i++;
             while(i<j && !Character.isDigit(cs[j]) && !Character.isLetter(cs[j])) j--;
             if(i >= j) break;
             String ss = cs[i] + "";
             String ss1 = cs[j] + "";
             if(!ss.equalsIgnoreCase(ss1))
                 return false;

             i++;
             j--;
         }
         return true;
     }
 }