Practice: Smallest Range of K Lists

This one is a bit tougher so don't feel bad if you don't finish. Again: the point is to demonstrate your thinking process and that you ask enough questions and think things through before you write any code.

Here’s the question:

You have k lists of sorted integers. Find the smallest range that includes at least one number from each of the k lists.

Here's some sample code

<span class="hljs-comment">// For example,</span>
list1 = [<span class="hljs-number">4</span>, <span class="hljs-number">10</span>, <span class="hljs-number">15</span>, <span class="hljs-number">24</span>, <span class="hljs-number">26</span>];
list2 = [<span class="hljs-number">0</span>, <span class="hljs-number">9</span>, <span class="hljs-number">12</span>, <span class="hljs-number">20</span>];
list3 = [<span class="hljs-number">5</span>, <span class="hljs-number">18</span>, <span class="hljs-number">22</span>, <span class="hljs-number">30</span>];