Fraction to Recurring Decimal LeetCode solution in Java

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class Solution {
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  public String fractionToDecimal(int numerator, int denominator) {
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    if (numerator == 0) {
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      return "0";
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    }
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    StringBuilder sb = new StringBuilder("");
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    if (numerator < 0 && denominator > 0 || numerator > 0 && denominator < 0) {
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      sb.append("-");
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    }
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    long divisor = Math.abs((long) numerator);
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    long dividend = Math.abs((long) denominator);
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    long remainder = divisor % dividend;
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    sb.append(divisor / dividend);
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    if (remainder == 0) {
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      return sb.toString();
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    }
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    sb.append(".");
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    HashMap<Long, Integer> map = new HashMap<Long, Integer>();
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    while (remainder != 0) {
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      if (map.containsKey(remainder)) {
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        sb.insert(map.get(remainder), "(");
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        sb.append(")");
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        break;
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      }
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      map.put(remainder, sb.length());
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      remainder *= 10;
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      sb.append(remainder / dividend);
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      remainder %= dividend;
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    }
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    return sb.toString();
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  }
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}