Smallest Range Covering Elements from K Lists

You have k lists of sorted integers in non-decreasing order. Your task is to find the smallest range that includes at least one number from each of the k lists. The range [a, b] is considered smaller than [c, d] if b - a is less than d - c, or if b - a is equal to d - c and a is less than c.

Constraints

• nums.length == k
• 1 <= k <= 3500
• 1 <= nums[i].length <= 50
• -10^5 <= nums[i][j] <= 10^5
• nums[i] is sorted in non-decreasing order.