Valid a Palindrome

 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 {/** * 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 static boolean isPalindrome(String s) {if (s == null || s.length() <= 0) {return true;}int start = 0;int end = s.length() - 1;while (start <= end) {char cur = s.charAt(start);char cur2 = s.charAt(end);if (cur < '0' || (cur > '9' && cur < 'A')|| (cur > 'Z' && cur < 'a') || cur > 'z') {start++;continue;}if (cur >= 'A' && cur <= 'Z') {System.out.println("Before conversion: " + cur);cur = (char) ((int) cur + 32);}if (cur2 < '0' || (cur2 > '9' && cur2 < 'A')|| (cur2 > 'Z' && cur2 < 'a') || cur2 > 'z') {end--;continue;}if (cur2 >= 'A' && cur2 <= 'Z') {cur2 = (char) ((int) cur2 + 32);}if (cur != cur2)return false;start++;end--;}return true;}}