What is the strategy to find the Top K Frequent Elements in an array?
This problem asks to return the k most frequent elements from an array. It tests heap usage or bucket sort techniques.
Why Interviewers Ask This
Interviewers use this to test frequency counting and selection algorithms. They want to see if you can combine hash maps with heaps or buckets to solve the problem efficiently. It demonstrates multi-step problem decomposition.
How to Answer This Question
Explain the two-step process: first, count frequencies using a hash map. Second, select the top K elements. For selection, discuss using a min-heap of size K to keep the largest elements, or bucket sort where indices represent frequencies. Compare time complexities: O(n log k) for heap, O(n) for bucket sort.
Key Points to Cover
- Frequency counting with hash map
- Min-heap selection strategy
- Bucket sort alternative
- Time complexity optimization
Sample Answer
First, I count the frequency of each element using a hash map. Then, to find the top K frequent elements, I can use a min-heap of size K. I iterate through the frequency map, pushing elements onto the heap. If the heap e…
Common Mistakes to Avoid
- Sorting all elements by frequency inefficiently
- Not handling ties in frequency correctly
- Incorrect heap size management
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