Merge k Sorted Lists
You are given an array of $k$ linked-lists, each sorted in ascending order. Merge all the linked-lists into one sorted linked list. Use a Min-Heap (Priority Queue) for an efficient solution.
Why Interviewers Ask This
Amazon asks this question to evaluate a candidate's mastery of advanced data structures and ability to optimize for scalability. Specifically, they test your capacity to move beyond naive solutions that degrade performance as input size grows. The interviewer looks for proficiency in using Min-Heaps to manage complexity efficiently, demonstrating the 'Invent and Simplify' leadership principle by finding elegant algorithmic shortcuts rather than brute-force methods.
How to Answer This Question
Key Points to Cover
- Demonstrating knowledge of O(N log k) vs O(N*k) time complexity trade-offs
- Correctly implementing the Min-Heap logic for dynamic element selection
- Handling null pointers and empty list edge cases gracefully
- Using a dummy node to simplify linked list construction logic
- Articulating space complexity as O(k) due to heap storage
Sample Answer
Common Mistakes to Avoid
- Failing to handle the case where one or more input lists are initially empty
- Attempting to merge lists sequentially without a heap, leading to TLE on large inputs
- Forgetting to re-insert the next node from the same list after extracting the current minimum
- Not explicitly stating the time and space complexity analysis during the solution walkthrough
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