<p>You have <code>k</code> lists of sorted integers in <strong>non-decreasing order</strong>. Find the <b>smallest</b> range that includes at least one number from each of the <code>k</code> lists.</p>
<p>We define the range <code>[a, b]</code> is smaller than range <code>[c, d]</code> if <code>b - a < d - c</code><strong>or</strong><code>a < c</code> if <code>b - a == d - c</code>.</p>