<p>Given an array of strings <code>words</code>, return <em>the smallest string that contains each string in</em><code>words</code><em>as a substring</em>. If there are multiple valid strings of the smallest length, return <strong>any of them</strong>.</p>
<p>You may assume that no string in <code>words</code> is a substring of another string in <code>words</code>.</p>