How should I practice Phone Spam Report Counter?

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Problem · Hash Table

Phone Spam Report Counter

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Problem statement

Process a finite ordered sequence of operations for a phone spam-report counter.

REPORT phoneNumber records one new spam report for phoneNumber. Repeated reports are distinct events, so each operation increments that number's count by one.
COUNT phoneNumber returns the current number of reports for phoneNumber. A number that has not been reported returns 0.

Return the integer results of all COUNT operations in encounter order. A REPORT operation produces no result. There is no deletion or time window.

Function

countSpamReports(operations: String[]) → int[]

Examples

Example 1

operations = ["REPORT 4155550100","REPORT 4155550100","COUNT 4155550100","COUNT 2125550199"]return = [2,0]

The first number receives two reports. The second number has never been reported.

Example 2

operations = ["COUNT 7","REPORT 7","COUNT 7","REPORT 8","REPORT 7","COUNT 8","COUNT 7"]return = [0,1,1,2]

Counts are independent per phone number and reflect only preceding REPORT operations.

Example 3

operations = ["REPORT 999","COUNT 999","COUNT 999"]return = [1,1]

A count query does not mutate the stored count.

Constraints

1 <= operations.length <= 100000.
Every operation is exactly REPORT phoneNumber or COUNT phoneNumber.
Every phoneNumber contains between 1 and 32 decimal digits.
The count for every phone number fits in a signed 32-bit integer.