Leetcode: 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
, '(');
res += ')';
return res;
}
record
= pos;
res += char(n * 10 / d + '0');
pos++;
n = (n * 10) % d;
}
return res;
}
};