LeetCode-166- Fraction to Recurring Decimal

算法描述：

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.

Example 1:

Input: numerator = 1, denominator = 2
Output: "0.5"

Example 2:

Input: numerator = 2, denominator = 1
Output: "2"

Example 3:

Input: numerator = 2, denominator = 3
Output: "0.(6)"

解题思路：模拟题。需要注意的点：1 正负号，2 溢出 ，3 小数点 ，4利用unordered_map判断重复

    string fractionToDecimal(int numerator, int denominator) {
        if(numerator==0) return "0";
        string res = "";
        if((numerator <0 && denominator > 0 ) || (numerator >0 && denominator <0)) res += "-";
        
        long long num1 = llabs(numerator);
        long long num2 = llabs(denominator);
        
        res += to_string(num1/num2);
        
        long long mo = num1%num2;
        
        
        if(mo == 0) return res;
        
        res += ".";
        
        unordered_map<int,int> unmap;
        
        while(mo > 0){
            if(unmap.find(mo)!=unmap.end()){
                res.insert(unmap[mo],1,'(');
                res += ")";
                break;
            }
            unmap[mo]=res.size();
            
            res += to_string(mo*10 / num2);
            mo = mo*10 % num2;
        }
        return res;
    }