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、用一個map來記錄n除以d的過程中被除數的變化，以及當被除數為n時相應的商在返回結果string中的位置，方便以後添加（。

  2、負數變正數的時候會越界，下面的例子2^31 = 2 147 483 648，int表示范圍（-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 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;
  	}
  };