166. 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)".

Hint:

1. No scary math, just apply elementary math knowledge. Still remember how to perform a long division?
2. Try a long division on 4/9, the repeating part is obvious. Now try 4/333. Do you see a pattern?
3. Be wary of edge cases! List out as many test cases as you can think of and test your code thoroughly.

Credits:

Special thanks to ​​@Shangrila​​ for adding this problem and creating all test cases.

class Solution {
public:
  string fractionToDecimal(int numerator, int denominator) {
    if (numerator == 0) return"0";
    string res;
    if (numerator < 0 ^ denominator < 0) res += '-';
    long long n = numerator;
    n=abs(n);
    long long d = denominator;
    d=abs(d);
    long long integer = n / d;
    res += to_string(integer);
    long long r = n%d;
    if (r != 0){
      res += '.';
    }
    else{
      return res;
    }
    map<long long, int> m;
    while (r){
      if (m.count(r)){
        res.insert(m[r], "(");
        res += ')';
        break;
      }
      m[r] = res.size();//记录出现该余数的位置
      r *= 10;
      res += to_string(r / d);

      r = r%d;
    }
    return res;
  }
};