Given k sorted integer arrays, merge them into one sorted array.

Example 1:

Input: 
[[1, 3, 5, 7],
 [2, 4, 6],
 [0, 8, 9, 10, 11]]

Output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

Example 2:

Input: [[1, 2, 3], [1, 2]]
Output: [1, 1, 2, 2, 3]

Although the algorithm was easy to solve. The interviewer drilled me more on runtime complexities.
Why Heap
What other approaches
etc