125. Valid Palindrome My Submissions Question

/*
125. Valid Palindrome My Submissions Question
Total Accepted: 94559 Total Submissions: 401331 Difficulty: Easy
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.

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*/



public class IsPalindrome {
    public static boolean isPalindrome(String s) {
        /* O (n) time, O(1) space
            The idead is simple, have two pointers - one at the head while teh other one at tail.
            Move them towards each other until they meet while skippig non-aplphanumeric 
            characters.

            Consider the case where given string contains only non-alphanumberic characters. This is
            a valid palindrome because the empty string is also a valid palindrome.
        */
        int i = 0, j = s.length() - 1;
        while (i < j) {
            while(i < j && !Character.isLetterOrDigit(s.charAt(i))) i++;
            while (i < j && ! Character.isLetterOrDigit(s.charAt(j))) j--;
            if (Character.toLowerCase(s.charAt(i))
                != Character.toLowerCase(s.charAt(j))) {
                return false;
            }
            i++; j--; 
        }
        return true;

    }

    public static boolean isPalindrome_int(int x) {
        if (x < 0) return false;
        int p=x, q=0;
        
        while(p>=10) {
            q *=10;   // q=0,  q=10  q=120
            q += p%10;  // if x=1221, 1221%10 => q = 1,  122%10=2 q=12   q=120+2=122
            p /=10;     //  p/10 => p= 122,    p/10 => p=12  p =1
        }
        return (p == x%10 && q == x/10);
    }
    
    public static void main(String[] args) {
        String str = "A man, a plan, a canal:Panama";

        int x = 121;
        int y = 1221;
        int z = 12321;
        int[] arr = {x, y,z};

        System.out.printf("%s is Palindrome string: %b\n", str, isPalindrome(str));
        
        for( int i : arr) { 
            System.out.println(isPalindrome_int(i));
        }

    }
}