leetcode题记——Valid 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.

class Solution {
    public boolean isPalindrome(String s) {
        char t[] = s.toCharArray();
        char a[] = new char[t.length];
        int l=0;
        for(int i=0;i<t.length;i++){
            if(t[i]>='a'&&t[i]<='z'||t[i]>='A'&&t[i]<='Z'||t[i]>='0'&&t[i]<='9'){
                if(t[i]>='A'&&t[i]<='Z')
                    a[l]= Character.toLowerCase(t[i]);
                    else
                        a[l]= t[i]; 
                l++;
            }
        }
        for(int i=0,j=l-1;i<=j;i++,j--){
            if(a[i]!=a[j])
                return false;
        }
        return true;
    }
}