Top K Frequent - Algorithm

Phase 1: Count frequencies using a hash map. Phase 2: Find the $k$ elements with highest frequency using a heap.

For phase 2, you can either:

• Use a min-heap of size $k$ (keep $k$ most frequent)
• Use a max-heap of all elements and extract $k$ times

The min-heap approach is $O(n \log k)$, better when $k$ is small. Time: $O(n \log k)$. Space: $O(n)$.