Constraints:

• $1\leq m \leq50$
• $0\leq$ lists[i].length $\leq 50$
• $-10^9\leq$ lists[i][j] $\leq 10^9$
• $1\leq$ k $\leq 10^9$

So far, you’ve probably brainstormed some approaches and have an idea of how to solve this problem. Let’s explore some of these approaches and figure out which one to follow based on considerations such as time complexity and any implementation constraints.

A naive approach to this problem can be to merge all the lists into a single list and then sort it to find the $k^{th}$ smallest number from it.

The time complexity of the naive approach is $O(n \log n)$ ...