Iterative-进制转换

    public String toHexspeak(String num) {
        StringBuffer sb = new StringBuffer();
        char[] chs = new char[]{‘A‘, ‘B‘, ‘C‘, ‘D‘, ‘E‘, ‘F‘};
        long n = Long.valueOf(num);
        while (n > 0) {
            int d = (int)(n % 16);
            if (d == 1) sb.append("I");
            else if (d == 0) sb.append("O");
            else if (d > 1 && d <= 9) return "ERROR";
            else sb.append(chs[d - 10]);
            n = n / 16;
        }
        return sb.reverse().toString();
    }

    public String convertToBase7(int num) {
        if (num == 0) return "0";
        StringBuffer sb = new StringBuffer();
        boolean flag = num >= 0;
        num = num >= 0 ? num : -num;
        while (num > 0) {
            int d = num % 7;
            sb.append(d);
            num = num / 7;
        }
        return flag ? sb.reverse().toString() : "-" + sb.reverse().toString();
    }