How should I practice Peak Concurrent Calls by UTC Day?

Start by reading the full statement, solve the visible examples, then compare the pattern against related HubSpot online assessment problems in FastPrep.

Is Peak Concurrent Calls by UTC Day associated with HubSpot?

FastPrep tags this as a HubSpot online assessment coding practice problem when the problem catalog has that company and stage context.

Problem · Intervals

Peak Concurrent Calls by UTC Day

Learn this problem

● Hard

HubSpotFULLTIMEOA

Problem statement

You are given records for completed phone calls. Record i belongs to customer customerIds[i], has unique identifier callIds[i], and is active during the half-open interval [startTimestamps[i], endTimestamps[i]). Timestamps are Unix milliseconds in UTC.

For every customer and every UTC date on which at least one of that customer's calls is active, find the maximum number of concurrent calls during that date.

Peak selection

Choose the earliest millisecond in the date at which the maximum concurrency is active.
A call ending at a timestamp is not active at that timestamp. A call starting at that timestamp is active.
Include exactly the call IDs active at the chosen timestamp, sorted lexicographically.

Return format

Return one string per customer-date pair in this exact format:

customerId|YYYY-MM-DD|maxConcurrentCalls|timestamp|callId1,callId2,...

Sort the returned strings by numeric customer ID, then by date. A call spanning midnight contributes independently to each UTC date it intersects.

Function

peakConcurrentCalls(customerIds: int[], callIds: String[], startTimestamps: long[], endTimestamps: long[]) → String[]

Examples

Example 1

customerIds = [1,1,1,2]callIds = ["A","B","C","X"]startTimestamps = [0,10,20,86399990]endTimestamps = [30,20,86400010,86400020]return = ["1|1970-01-01|2|10|A,B","1|1970-01-02|1|86400000|C","2|1970-01-01|1|86399990|X","2|1970-01-02|1|86400000|X"]

Customer 1 first reaches two active calls at timestamp 10. Call C continues into the next UTC date. Customer 2's call also crosses midnight, so both customers have a record for 1970-01-02.

Example 2

customerIds = [7,7]callIds = ["left","right"]startTimestamps = [100,200]endTimestamps = [200,300]return = ["7|1970-01-01|1|100|left"]

The first call ends exactly when the second begins, so the half-open intervals never overlap. The earliest timestamp with the maximum concurrency of 1 is 100.

Example 3

customerIds = [4,4]callIds = ["before","after"]startTimestamps = [86399999,86400000]endTimestamps = [86400000,86400001]return = ["4|1970-01-01|1|86399999|before","4|1970-01-02|1|86400000|after"]

The call ending at midnight belongs only to 1970-01-01. The call starting at midnight belongs to 1970-01-02.

Constraints

1 <= customerIds.length <= 100000
All four input arrays have the same length.
1 <= customerIds[i] <= 10^9
Every callIds[i] is unique, nonempty, and contains only ASCII letters, digits, underscores, or hyphens.
0 <= startTimestamps[i] < endTimestamps[i] <= 4102444800000
Across all calls, the total number of intersected UTC dates is at most 200000.