p125

 
public class  {
    public boolean isPalindrome(String s) {
        char[] a = s.toCharArray();
		int len = a.length;

		for (int l = 0, r = len - 1; l < r; l++, r--) {
			while (!check(a[l]) && l < r)
				l++;
			while (!check(a[r]) && l < r)
				r--;
			if (a[l] == a[r]
					|| ((a[l] < '0' || a[l] > '9') && Math.abs(a[l] - a[r]) == 32)) 
				continue;

			return false;
		}
		return true;
	}

	public boolean check(char a) {
		return (a >= 'A' && a <= 'Z') || (a >= 'a' && a <= 'z')
				|| (a >= '0' && a <= '9');
	}
}