【Leetcode】Valid Palindrome

题目链接：https://leetcode.com/problems/valid-palindrome/

题目：

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.

算法：

 public boolean isDecent(char c) {
         if (Character.isAlphabetic(c) || Character.isDigit(c)) {
             return true;
         } else
             return false;
     }

     public boolean isPalindrome(String s) {
         char c[] = s.toLowerCase().toCharArray();
         int i = 0, j = c.length - 1;
         while (i < j) {
             if (isDecent(c[i]) && isDecent(c[j])) {
                 if (c[i] == c[j]) {
                     i++;
                     j--;
                 } else {
                     return false;
                 }
             }
             if (!isDecent(c[i])) {
                 i++;
             }
             if (!isDecent(c[j])) {
                 j--;
             }
         }
         return true;
     }