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
﻿public class Solution {
    public string FractionToDecimal(int numerator, int denominator) {
        if (numerator == 0) {
            return "0";
        }
        StringBuilder sb = new StringBuilder();
        bool neg = (numerator > 0) ^ (denominator > 0);
        sb.Append(neg ? "-" : "");
        long a = Math.Abs((long)numerator), b = Math.Abs((long)denominator);
        sb.Append(a / b);
        a %= b;
        if (a == 0) {
            return sb.ToString();
        }
        sb.Append(".");
        Dictionary<long, int> d = new Dictionary<long, int>();
        while (a != 0) {
            d[a] = sb.Length;
            a *= 10;
            sb.Append(a / b);
            a %= b;
            if (d.ContainsKey(a)) {
                sb.Insert(d[a], "(");
                sb.Append(")");
                break;
            }
        }
        return sb.ToString();
    }
}