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)".

Analyse: Use hash to store the fractional and its corresponding position at result. If the fractional has occurred, the result is recurring; If the fractional is 0, return current result. 

Runtime: 0ms.

class Solution {
public:
    string fractionToDecimal(int numerator, int denominator) {
        if(!numerator) return "0";
        
        string result;
        unordered_map<int, int> um;
        if(numerator < 0 ^ denominator < 0) result += '-';
        long long int nu = numerator, de = denominator;
        nu = abs(nu);
        de = abs(de);
        
        result += to_string(nu / de);
        long long int fractional = nu % de;
        if(!fractional) return result;
        result += ".";
        
        while(fractional) {
            // find if the fractional is in um
            if(um.find(fractional) != um.end()) {
                result.insert(um[fractional], "(");
                result += ")";
                return result;
            }
            
            // push the fractional and its position in result into um
            um[fractional] = result.length();
            
            fractional *= 10;
            result += to_string(fractional / de);
            fractional %= de;
        }
        return result;
    }
};