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,
Solution:
1、用一个map来记录n除以d的过程中被除数的变化，以及当被除数为n时相应的商在返回结果string中的位置，方便以后添加（。
2、负数变正数的时候会越界，，下面的例子2^31 = 2 147 483 648，int表示范围（-2147483648~2147483647），所以要用long long：
Input:-1, -2147483648
Output:"0.0000000000000000000000000000001"
Expected:"0.0000000004656612873077392578125"
class Solution {public:string fractionToDecimal(int numerator, int denominator) {string res = "";if (numerator == 0) return "0";if (denominator == 0)return res;long long n = numerator;long long d = denominator;if ((n < 0 && d > 0) || (n > 0 && d < 0))res = "-";if (n < 0) n = -n;if (d < 0) d = -d;res += to_string(n / d);n = n%d;if (n == 0) return res;res += '.';int pos = res.size();map<long long, int> record;while (n != 0) {if (record.find(n) != record.end()) {res.insert(res.begin() + record[n], '(');res += ')';return res;}record[n] = pos;res += char(n * 10 / d + '0');pos++;n = (n * 10) % d;}return res;}};
我就想是一只草原中被牧童遗忘的羊，
