415. Valid Palindrome【LintCode java】

Description

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

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.

Example

"A man, a plan, a canal: Panama" is a palindrome.

"race a car" is not a palindrome.

Challenge

O(n) time without extra memory.

解题：判断某字符串是否是回文字符串，其中标点可以不对称，但字母和数字必须要对称。可以通过Character中的函数， isLetterOrDigit( char ch )来判断。代码如下：

public class Solution {
    /**
     * @param s: A string
     * @return: Whether the string is a valid palindrome
     */
    public boolean isPalindrome(String s) {
        // write your code here
        s = s.toUpperCase();
        for(int i = 0, j = s.length() - 1; i <= j; i++, j--){
            if(s.charAt(i) == s.charAt(j))
                continue;
            else{
                if(Character.isLetterOrDigit(s.charAt(i)) && Character.isLetterOrDigit(s.charAt(j)))
                    return false;
                else{
                    if(Character.isLetterOrDigit(s.charAt(i))){
                        i--;
                    }else if(Character.isLetterOrDigit(s.charAt(j))){
                        j--;
                    }else{
                        continue;
                    }
                }
            }
        }
        return true;
    }
}