He had clearly stated that this could be done using a normal sorting algorithm in O(n log n), but I had to provide a more optimized solution.

I proposed a solution using a stack, which somehow worked for the test case he gave me. However, he proved it wrong and provided a hint to use another data structure. I understood the hint and realized it was to be done using a min-heap. The time complexity of this approach was O(n log k).

He had clearly stated that this could be done using a normal sorting algorithm in O(n log n), but I had to provide a more optimized solution.

I proposed a solution using a stack, which somehow worked for the test case he gave me. However, he proved it wrong and gave me a hint to use another data structure. I understood the hint and realized it was to be done using a min-heap. The time complexity of that approach was O(n log k)!