287. Merge K Sorted Lists

Given k sorted lists (arrays), merge them into one globally sorted array.

A brute-force approach is to flatten everything and sort once, but interviewers usually expect a better merge strategy that uses the fact each list is already sorted.

Requirements

Implement:

function mergeKSortedLists(lists) {}

Behavior expectations:

• Handle empty input and empty inner lists
• Preserve duplicates
• Support negative and positive numbers
• Return deterministic sorted output

Example Usage

mergeKSortedLists([
  [1, 4, 5],
  [1, 3, 4],
  [2, 6],
]); // [1, 1, 2, 3, 4, 4, 5, 6]

mergeKSortedLists([]); // []