private String check1(String s, int l, int r) {
		int i = 1;
		for (; l - i >= 0; i++) {
			if (s.charAt(l - i) != s.charAt(r + i))
				break;
		}

		if (l - i >= 0)
			return null;
		StringBuilder sb = new StringBuilder(s.substring(r + i));
		sb.reverse();
		return sb + s;
	}