Fraction to Recurring Decimal
<p>Given two integers representing the <code>numerator</code> and <code>denominator</code> of a fraction, return <em>the fraction in string format</em>.</p>

<p>If the fractional part is repeating, enclose the repeating part in parentheses.</p>

<p>If multiple answers are possible, return <strong>any of them</strong>.</p>

<p>It is <strong>guaranteed</strong> that the length of the answer string is less than <code>10<sup>4</sup></code> for all the given inputs.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> numerator = 1, denominator = 2
<strong>Output:</strong> &quot;0.5&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> numerator = 2, denominator = 1
<strong>Output:</strong> &quot;2&quot;
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> numerator = 4, denominator = 333
<strong>Output:</strong> &quot;0.(012)&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>-2<sup>31</sup> &lt;=&nbsp;numerator, denominator &lt;= 2<sup>31</sup> - 1</code></li>
	<li><code>denominator != 0</code></li>
</ul>
Hash Table; Math; String
func fractionToDecimal(numerator int, denominator int) string {
	if numerator == 0 {
		return "0"
	}
	ans := ""
	if (numerator > 0) != (denominator > 0) {
		ans += "-"
	}
	a := int64(numerator)
	b := int64(denominator)
	a = abs(a)
	b = abs(b)
	ans += strconv.FormatInt(a/b, 10)
	a %= b
	if a == 0 {
		return ans
	}
	ans += "."
	d := make(map[int64]int)
	for a != 0 {
		if pos, ok := d[a]; ok {
			ans = ans[:pos] + "(" + ans[pos:] + ")"
			break
		}
		d[a] = len(ans)
		a *= 10
		ans += strconv.FormatInt(a/b, 10)
		a %= b
	}
	return ans
}

func abs(x int64) int64 {
	if x < 0 {
		return -x
	}
	return x
}