How should I practice VIP and Regular Service Scheduler?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Intuit phone screen problems in FastPrep.

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VIP and Regular Service Scheduler

Intuit● MediumFULLTIMEPHONE SCREEN

Problem statement

Source note: The report says the first part of this phone screen was coding: design and build a scheduler for an in-person service center, where walk-in customers check in, get a ticket with the next service number, and staff call them in the order the scheduler picks. There are two kinds of customers, regular and VIP, and VIPs get higher priority. The candidate was asked to sketch Customer and ServiceScheduler classes, first serve every VIP before any regular through check-in and get-next methods, and then change get-next to keep a 2:1 VIP-to-regular rate. Next to the rate it gives a 100-to-50 example of that ratio.

The report does not say how the two versions are called, what get-next returns when nobody waits, or exactly how the 2:1 rate behaves when one kind runs out. Practice choices: one function replays check-in and call events under either policy, tickets are shared and start at 1, an empty call returns -1, customers of one kind are called in check-in order, and the 2:1 rate counts VIPs since the last regular, falls back to whichever kind is waiting, resets only when a regular is called, and ignores empty calls. The event and length limits are also practice choices.

The judged task matches the report at about 85%.

A walk-in service center gives each customer who checks in a ticket with the next service number, starting at 1. Ticket numbers are shared by both kinds of customers. Staff then call customers one at a time, in the order a scheduler decides. Customers are either VIP or regular, and within each kind they are always called in check-in order.

Process events in order. "VIP" and "REGULAR" check in one customer of that kind. "NEXT" calls the next customer and records their ticket number, or -1 if nobody is waiting. The scheduler follows policy:

"VIP_FIRST": call a waiting VIP whenever there is one. Call a regular only when no VIP is waiting.
"TWO_TO_ONE": serve VIPs and regulars at a 2:1 rate. Count the VIPs called since the last regular was called. If a VIP is waiting and that count is below 2, call the VIP. If the count has reached 2 and a regular is waiting, call the regular, and the count starts over at 0. If only one kind is waiting, call that kind; calling a regular always resets the count, and calling a VIP always adds one to it. A "NEXT" that finds nobody waiting changes nothing.

Return the recorded results of all "NEXT" events, in order.

Function

serveCustomers(policy: String, events: String[]) → int[]

Examples

Example 1

policy = "VIP_FIRST"events = ["REGULAR","VIP","REGULAR","VIP","NEXT","NEXT","NEXT","NEXT","NEXT"]return = [2,4,1,3,-1]

Tickets 1 to 4 go to a regular, a VIP, a regular and a VIP. Under VIP_FIRST both VIPs are called first, in arrival order (tickets 2 and 4), then the regulars (tickets 1 and 3). The fifth call finds nobody waiting and returns -1.

Example 2

policy = "TWO_TO_ONE"events = ["VIP","VIP","VIP","REGULAR","REGULAR","VIP","NEXT","NEXT","NEXT","NEXT","NEXT","NEXT"]return = [1,2,4,3,6,5]

VIPs hold tickets 1, 2, 3 and 6 and regulars hold 4 and 5. The calls go VIP, VIP, regular, VIP, VIP, regular: tickets 1, 2, 4, 3, 6, 5. After two VIPs in a row, a waiting regular is always next.

Example 3

policy = "TWO_TO_ONE"events = ["REGULAR","REGULAR","NEXT","VIP","NEXT","NEXT","NEXT"]return = [1,3,2,-1]

No VIP is waiting at the first call, so regular ticket 1 is called and the VIP streak stays at 0. VIP ticket 3, who checked in after that call, is called next. Then regular ticket 2 is the only one waiting. The last call finds nobody and returns -1.

Constraints

policy is "VIP_FIRST" or "TWO_TO_ONE"
1 <= events.length <= 2000
Each event is "VIP", "REGULAR" or "NEXT", and at least one event is "NEXT".