static String toHex(int n) {    Deque<Character> stack = new LinkedList<>();    int remain = n;    do {        int i = remain % 16;        char str = i > 10 ? (char) ('A' + (i - 10)) : (char) (i + '0');        stack.addLast(str);        remain = remain / 16;    } while (remain != 0);    StringBuilder sb = new StringBuilder();    while (!stack.isEmpty()) {        sb.append(stack.pollLast());    }    return sb.toString();}