beingsde
Sign In
Back to all DSA patterns
HashMap / Heap•Pattern: HashMap + Heap / Bucket Sort•Medium

Top K frequent elements

Problem Intuition & Objective

Return the k most frequently occurring elements.

Time ComplexityO(n log k) heap; O(n) bucket
Optimal
Space ComplexityO(n)
Memory Bounds
Optimal Algorithmic Approach

HashMap + Min-heap of size k, or bucket sort for O(n).

Core Invariants & Edge Cases

  • Count frequencies in a HashMap
  • Use a min-heap of size k; evict least frequent
  • Bucket sort alternative: O(n) using frequency as bucket index
Previous ProblemGroup anagrams togetherNext Problem Longest substring without repeating characters

System Design & Architecture Roadmap

Coding interviews are only 50% of the bar. Master High-Level Design, distributed systems, and Object-Oriented LLD.

60+ HLD QuestionsSharding, caching, and real-time distributed systems.27 LLD BlueprintsObject-oriented design patterns with class diagrams.SDE Quick ReferenceLatency numbers and database selection matrix.