[LeetCode] #125 Valid Palindrome

这题超烦@_@

public class Solution {
    public boolean isPalindrome(String s) {
        if (s == null) {
            return false;
        }
        int start = 0;
        int end = s.length() - 1;
        while (start < end) {
            while (start < end && !isValid(s.charAt(start))) {
                start++;
            }
            while (start < end && !isValid(s.charAt(end))) {
                end--;
            }
            if (start < end && !equalsIgnoreCase(s.charAt(start), s.charAt(end))) {
                return false;
            }
            start++;
            end--;
        }
        return true;
    }
    
    private boolean equalsIgnoreCase(char a, char b) {
        if (a == b) {
            return true;
        }
        if (isChar(a) && isChar(b) && Math.abs(a - b) == Math.abs('A' - 'a')) {
            return true;
        }
        return false;
    }
    
    private boolean isValid(char a) {
        return isChar(a) || (a >= '0' && a <= '9');
    }
    
    private boolean isChar(char a) {
        if (a >= 'a' && a <= 'z') {
            return true;
        }
        if (a >= 'A' && a <= 'Z') {
            return true;
        }
        return false;
    }
}

Character.toLowerCase() would make it easier :P