<p>You are given a list of airline <code>tickets</code> where <code>tickets[i] = [from<sub>i</sub>, to<sub>i</sub>]</code> represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it.</p>
<p>All of the tickets belong to a man who departs from <code>"JFK"</code>, thus, the itinerary must begin with <code>"JFK"</code>. If there are multiple valid itineraries, you should return the itinerary that has the smallest lexical order when read as a single string.</p>
<ul>
<li>For example, the itinerary <code>["JFK", "LGA"]</code> has a smaller lexical order than <code>["JFK", "LGB"]</code>.</li>
</ul>
<p>You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once.</p>
<strong>Explanation:</strong> Another possible reconstruction is ["JFK","SFO","ATL","JFK","ATL","SFO"] but it is larger in lexical order.
