/*
 * @lc app=leetcode id=125 lang=java
 *
 * [125] Valid Palindrome
 */

// @lc code=start
class Solution {
    public boolean isPalindrome(String s) {
        int i = 0, j = s.length()-1;
        boolean r = true;
        while(i < j) {
            while(i<j && !isAlphanumberic(s.charAt(i))) {
                i++;
            }
            while(i<j && !isAlphanumberic(s.charAt(j))) {
                j--;
            }
            if(i>=j) {
                break;
            }
            if(!isSameLeterIgnoreCase(s.charAt(i), s.charAt(j))) {
                r = false;
                break;
            }
            i++;
            j--;
        }
        return r;
    }

    private boolean isAlphanumberic(char c) {
        return isAlpha(c) || isNumberic(c);
    }
    
    private boolean isAlpha(char c) {
        return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z';
    }

    private boolean isNumberic(char c) {
        return c >= '0' && c <= '9';
    }

    private boolean isSameLeterIgnoreCase(char a, char b) {
        return isNumberic(a) && a == b || isAlpha(a) && isAlpha(b) && Character.toLowerCase(a) == Character.toLowerCase(b);
    }
}
// @lc code=end