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;
    }
}