Fraction to Recurring Decimal

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)".

--------------------------------------------------- thinking --------------------------------------------------------------------

This problem should use hash table to record if a numerator has been repeating or not. Remember the interface of unordered_map<int, int>. And the hash key should be the numerator, while the value should be the position of current numerator!

-------------------------------------------------- problems ------------------------------------------------------------------

the overflow problem should be considered here!!! the plus-minus sign should also be considered here!! So it's very important to change the type from "int" to "long"

----------------------------------------------  codes --------------------------------------------------------------------------

class Solution {

public:

    string fractionToDecimal(int numerator, int denominator) {

        string result = "";

        if (numerator == 0) {

            return "0";

        }

        //calc symble

        if ((numerator<0)^(denominator<0)) {

            result += "-";

        }

        long n = abs(long(numerator));

        long d = abs(long(denominator));

        long r = n / d;

        result += to_string(r);

        if (n%d == 0) {

            return result;

        }

        result += ".";

        unordered_map<int, int> map;

        r = n % d;

        while (r) {

            if (map.count(r) > 0) {

                result.insert(map[r], 1, '(');

                result += ')';

                return result;

            }

            map[r] = result.size();

            r *= 10;

            long cur = r / d;

            result += to_string(cur);

            r = r % d;

        }

        return result;

    }

};