N-Repeated Element in Size 2N Array
<p>You are given an integer array <code>nums</code> with the following properties:</p>

<ul>
	<li><code>nums.length == 2 * n</code>.</li>
	<li><code>nums</code> contains <code>n + 1</code> <strong>unique</strong> elements.</li>
	<li>Exactly one element of <code>nums</code> is repeated <code>n</code> times.</li>
</ul>

<p>Return <em>the element that is repeated </em><code>n</code><em> times</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1,2,3,3]
<strong>Output:</strong> 3
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [2,1,2,5,3,2]
<strong>Output:</strong> 2
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> nums = [5,1,5,2,5,3,5,4]
<strong>Output:</strong> 5
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>2 &lt;= n &lt;= 5000</code></li>
	<li><code>nums.length == 2 * n</code></li>
	<li><code>0 &lt;= nums[i] &lt;= 10<sup>4</sup></code></li>
	<li><code>nums</code> contains <code>n + 1</code> <strong>unique</strong> elements and one of them is repeated exactly <code>n</code> times.</li>
</ul>
Array; Hash Table
function repeatedNTimes(nums: number[]): number {
    const s: Set<number> = new Set();
    for (const x of nums) {
        if (s.has(x)) {
            return x;
        }
        s.add(x);
    }
}
