LeetCode - Fraction to Recurring Decimal

Question Definition

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

• Given numerator = 1, denominator = 2, return “0.5”.
• Given numerator = 2, denominator = 1, return “2”.
• Given numerator = 2, denominator = 3, return “0.(6)”.

  Java Solution

  public String fractionToDecimal(int numerator, int denominator) {
    StringBuilder result = new StringBuilder();
    String sign = (numerator < 0 == denominator < 0 || numerator == 0) ? "" : "-";
    long num = Math.abs((long) numerator);
    long den = Math.abs((long) denominator);
    result.append(sign);
    result.append(num / den);
    long remainder = num % den;
    if (remainder == 0)
        return result.toString();
    result.append(".");
    HashMap<Long, Integer> hashMap = new HashMap<Long, Integer>();
    while (!hashMap.containsKey(remainder)) {
        hashMap.put(remainder, result.length());
        result.append(10 * remainder / den);
        remainder = 10 * remainder % den;
    }
    int index = hashMap.get(remainder);
    result.insert(index, "(");
    result.append(")");
    return result.toString().replace("(0)", "");
  }