Leetcode159： 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)".

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;      }};