leetcode166 Fraction to Recurring Decimal

思路：

模拟。

实现：

 class Solution
 {
 public:
     string fractionToDecimal(int numerator, int denominator)
     {
         long long a = numerator, b = denominator;
         string ans = "";
         if (a * b < ) ans += '-';
         a = abs(a); b = abs(b);
         ans += to_string(a / b);
         a %= b;
         if (!a) return ans;
         ans += '.';
         a *= ;
         vector<long long> v;
         map<pair<long long, long long>, int> mp;
         long long rem = a % b, q = a / b;
         while (rem && !mp.count(make_pair(rem, q)))
         {
             v.push_back(q);
             mp[make_pair(rem, q)] = v.size() - ;
             rem *= ;
             q = rem / b;
             rem %= b;
         }
         if (rem == )
         {
             v.push_back(q);
             for (auto it: v) ans += to_string(it);
         }
         else
         {
             int start = mp[make_pair(rem, q)];
             for (int i = ; i < start; i++) ans += to_string(v[i]);
             ans += '(';
             for (int i = start; i < v.size(); i++) ans += to_string(v[i]);
             ans += ')';
         }
         return ans;
     }
 };