Which optimized hashing pattern solves this lesson cleanly?

Question

Which optimized hashing pattern solves this lesson cleanly?

Option A — Correct answer

Frequency map followed by an order-preserving scan.

Option B

Plain nested loops without stored state

Option C

Two pointers after sorting every time

Option D

Stack matching only

Explanation

Frequency map followed by an order-preserving scan.

First Unique Character - Frequency Map Pattern Practice Quiz