20220606 Mathematics: fraction to decimal

        Title Description ： Given two integers , Molecules representing fractions respectively  numerator  Denominator  denominator, With   Returns a decimal as a string  . If the decimal part is a circular decimal , The loop is enclosed in brackets . If there are multiple answers , Just go back   Any one  . For all given inputs , Guarantee   The length of the answer string is less than  10^4 .

        coded ：

    public String fractionToDecimal(int numerator, int denominator) {
        if (denominator == 0) {
            return "";
        }
        if (numerator == 0) {
            return "0";
        }
        StringBuilder result = new StringBuilder();
        long num = numerator,den = denominator;

        if ((num >= 0) ^ (den >= 0)) {
            result.append("-");
        }
        num = Math.abs(num);
        den = Math.abs(den);

        result.append(num / den);
        num %= den;
        if (num == 0) {
            return result.toString();
        }

        result.append(".");
        int index = result.length() - 1;
        Map<Long, Integer> record = new HashMap<>();
        while (num != 0 && !record.containsKey(num)) {
            record.put(num, ++index);
            num *= 10;
            result.append(num / den);
            num %= den;
        }
        if (record.containsKey(num)) {
            result.insert(record.get(num), "(");
            result.append(")");
        }
        return result.toString();
    }