You are given $k$ sorted lists of integers, nums, where each list in nums is in non-decreasing order. Your task is to find the smallest range that contains at least one element from each of the $k$ lists.

A range $[a,b]$ is considered smaller than another range $[c,d]$ if $b−a<d−c$, or $a < c$ if $b-a==d-c$ ...