166. Fraction to Recurring Decimal

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)".

class Solution {
public:

    string fractionToDecimal(int numerator, int denominator)
    {
        return fractionToDecimalCore(numerator,denominator);
    }
    string fractionToDecimalCore(int64_t numerator,int64_t denominator) {
        if(numerator == 0)
            return "0";
        string ret;
        
        //determine the sign using xor
        if(numerator<0 ^ denominator<0)
            ret+="-";
        numerator = abs(numerator);
        denominator = abs(denominator);
        
        //append the integral part
        ret+=to_string(numerator/denominator);
        
        //in case,there is no fractional part
        if(numerator%denominator ==0)
            return ret;
        
        //add the decimal point
        ret+=".";
        
        unordered_map<int,int> map;
        for(int64_t remainder = numerator%denominator;remainder;remainder%=denominator)
        {
            //we find a repeating remainder
            if(map.count(remainder) > 0)
            {
                ret.insert(map[remainder],1,'(');
                ret+=')';
                break;
            }
            
            map[remainder] = ret.size();
            
            remainder*=10;
            ret+=to_string(remainder / denominator);
        }
        
        return ret;
        
        
        
    }
};