CareerCup

do manual division and if the remainder reapears the pattern will repeat. The code below will put the repeating sequence in "()" e.g. 1/3 = 0.(3), 4 / 3 = 1.(3), 1/6 = 0.1(6)

public String fractionToDecimal(int numerator, int denominator) {
    StringBuilder sb = new StringBuilder();
    if((numerator < 0) ^ (denominator < 0)) sb.append("-");
    long num = Math.abs((long)numerator);
    long den = Math.abs((long)denominator);
    long rem = num % den;
    sb.append(num / den);
    if(rem > 0) {
        sb.append(".");
        HashMap<Integer, Integer> seenRemDigitIdx = new HashMap<>();
        while(rem != 0) {
            int lastSeen = seenRemDigitIdx.getOrDefault((int)rem, -1);
            if(lastSeen != -1) {
                sb.insert(lastSeen, '(');
                sb.append(')');
                break;
            }
            seenRemDigitIdx.put((int)rem, sb.length());
            rem *= 10;
            sb.append(rem / den);
            rem = rem % den;
        }
    } else if(sb.toString().equals("-0")) {
        return "0";
    }
    return sb.toString();
}

public class Solution {
  public String getRepetitivePattern(int dividend, int divisor) {
    if(divisor == 0 || dividend % divisor = 0) {
      return null; // There is no pattern
    }
    dividend = Math.Abs(dividend);
    divisor = Math.Abs(divisor);
    dividend = (dividend % divisor) * 10;
    StringBuilder sb = new StringBuilder();
    // Map of dividend to starting index of pattern
    Map<Integer, Integer> cache = new HashMap<>();
    int newDividend = dividend, quotient = 0;
    // Return null in case we can never find a pattern
    while(cache.size() < Integer.MAX_VALUE) {
      quotient = (int)(dividend / divisor);
      if(cache.contains(newDividend)) {
        return sb.substring(cache.get(newDividend));
      }
      if (!cache.contains(newDividend)) {
        cache.put(newDividend, substring.length());
        substring.append(quotient);
      }
      newDividend = (dividend % divisor) * 10;
    }
    return null;
  }
}