Counter · Interview Problem

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Leetcode

Medium

Hash Maps

Design

Google

Counter

Design a counter that supports updating counts for string keys and querying them efficiently.

Acceptance 0%

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Problem Statement

Problem

Implement a counter data structure that stores integer counts for string keys.

Support operations to:

increase the count for a key by 1
decrease the count for a key by 1, removing the key if its count becomes 0
return the current count for a key

The counter should behave like a mutable in-memory frequency table.

Notes

If a key does not exist, its count is considered 0.
Decrementing a missing key should have no effect.
All operations should be efficient.

Input Format

A sequence of operations on a counter object, each operating on a string key.

Output Format

Return the result of each query operation, and keep internal state updated after each modification.

Constraints

Keys are non-empty strings.
Counts are integers and never negative.
Operations should be near O(1) on average.

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