HARD NC#44 Blind #43 Linked List
23. Merge k Sorted Lists
📖 Problem
You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it.
🧠 Visual Learning Aid
1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases
JS/TS Refreshers
- •Array methods (`push`, `pop`, `shift`, `slice`)
- •Object/Map/Set usage patterns
- •Function parameter and return typing
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
💡 Approach
- → Use divide and conquer strategy
- → Pairwise merge lists in each iteration
- → Keep reducing number of lists until only one remains
- → Time: O(n log k) where n is total nodes, Space: O(1) excluding result
🧭 Prerequisites
🛠️ Hints & Pitfalls
Hints
- •Use divide and conquer strategy
- •Pairwise merge lists in each iteration
- •Keep reducing number of lists until only one remains
Common Pitfalls
- •Time: O(n log k) where n is total nodes, Space: O(1) excluding result
🧪 Test Cases
Hidden tests on submit: 1
Test Case 1
Not run Input:
mergeKLists([arrayToList([1,4,5]), arrayToList([1,3,4]), arrayToList([2,6])]); Expected:
{"val":1,"next":{"val":1,"next":{"val":2,"next":{"val":3,"next":{"val":4,"next":{"val":4,"next":{"val":5,"next":{"val":6,"next":null}}}}}}}} Test Case 2
Not run Input:
mergeKLists([]); Expected:
null Test Case 3
Not run Input:
mergeKLists([arrayToList([])]); Expected:
null 📝 Code Editor
📤 Output