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.

 1 class Solution {
 2 public:
 3     string fractionToDecimal(int numerator, int denominator) {
 4         if(!numerator) return "0";
 5         
 6         string result;
 7         unordered_map<int, int> um;
 8         if(numerator < 0 ^ denominator < 0) result += '-';
 9         long long int nu = numerator, de = denominator;
10         nu = abs(nu);
11         de = abs(de);
12         
13         result += to_string(nu / de);
14         long long int fractional = nu % de;
15         if(!fractional) return result;
16         result += ".";
17         
18         while(fractional) {
19             // find if the fractional is in um
20             if(um.find(fractional) != um.end()) {
21                 result.insert(um[fractional], "(");
22                 result += ")";
23                 return result;
24             }
25             
26             // push the fractional and its position in result into um
27             um[fractional] = result.length();
28             
29             fractional *= 10;
30             result += to_string(fractional / de);
31             fractional %= de;
32         }
33         return result;
34     }
35 };