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)".

import java.util.HashMap;

public class Solution {
	public String fractionToDecimal(int numerator, int denominator) {
		if (numerator == 0) {
			return "0";
		}
		StringBuilder res = new StringBuilder();
		// "+" or "-"
		res.append(((numerator > 0) ^ (denominator > 0)) ? "-" : "");
		long num = Math.abs((long) numerator);
		long den = Math.abs((long) denominator);

		// integral part
		res.append(num / den);
		num %= den;
		if (num == 0) {
			return res.toString();
		}

		// fractional part
		res.append(".");
		HashMap<Long, Integer> map = new HashMap<Long, Integer>();
		map.put(num, res.length());
		while (num != 0) {
			num *= 10;
			res.append(num / den);
			num %= den;
			if (map.containsKey(num)) {
				int index = map.get(num);
				res.insert(index, "(");
				res.append(")");
				break;
			} else {
				map.put(num, res.length());
			}
		}
		return res.toString();
	}
	public static void main(String[] args) {
		Solution solution = new Solution();
		String res = solution.fractionToDecimal(1, 3);
		System.out.println(res);
	}
}

https://leetcode.com/discuss/23079/my-clean-java-solution