Leetcode 2671. Frequency Tracker

Design a data structure that supports add(number), deleteOne(number), and hasFrequency(f) queries—returning whether any value currently appears exactly f times—under up to 2e5 operations, so each operation must be efficient. The typical solution tracks value->count and count->number-of-values (e.g., two hash maps) to update counts and answer hasFrequency in constant time.