Hash Lookup & Counting · Hash map lookup / complement
Two Sum
LeetCode 1 · Module: Arrays & Hashing
The scenario
you are processing a stream of events and need fast memory of what has already happened — a seen value, a running count, or a reusable prefix state.
What you'll learn
- How to recognize the Hash Lookup & Counting pattern from the problem statement.
- The BASIC Framework breakdown for this problem.
- A clean, interview-ready Python solution with time/space analysis.
Full video, code, and the workspace are part of PatternMastery Pro — 500 problems for one $9.99 payment.