How do you merge K sorted lists into one sorted list?
This problem requires merging multiple sorted linked lists into a single sorted list. It tests heap usage or divide-and-conquer strategies.
Why Interviewers Ask This
This question evaluates a candidate's ability to handle multiple data streams efficiently. Interviewers look for the use of a min-heap to always pick the smallest available element. It tests priority queue implementation and time complexity analysis for large datasets.
How to Answer This Question
Explain the brute force approach of collecting all elements and sorting, noting its inefficiency. Propose the min-heap approach: insert the head of each list into a heap. Repeatedly extract the minimum and add the next node from that list to the heap. Alternatively, discuss divide-and-conquer merging pairs of lists. Compare time complexities of both methods.
Key Points to Cover
- Min-heap utilization
- Extract-min operation
- Insertion of next nodes
- Time complexity O(N log K)
Sample Answer
To merge K sorted lists efficiently, I would use a min-heap. Initially, I push the head of each non-empty list into the heap. Then, I repeatedly extract the minimum element from the heap and append it to the result list.…
Common Mistakes to Avoid
- Sorting all elements individually
- Incorrect heap initialization
- Forgetting to handle empty lists
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