How should I practice Concurrent Discounted Card Purchases?

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

Is Concurrent Discounted Card Purchases associated with Brex?

FastPrep tags this as a Brex phone screen coding practice problem when the problem catalog has that company and stage context.

Problem · Simulation

Concurrent Discounted Card Purchases

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BrexFULLTIMEPHONE SCREEN

Problem statement

A player has gem balances in the fixed color order [B,W,G,R,Y]. Each row cards[i] is [rewardColor,costB,costW,costG,costR,costY], where rewardColor is an index from 0 through 4.

The player may own multiple copies of a card. Before a purchase, each already-owned card of color c discounts that purchase's cost in color c by one gem, but a cost never falls below zero.

Each request is [expectedVersion,cardIndex]. Requests are serialized in array order for this player. Return -1 for a version conflict, 0 when the discounted card is unaffordable, and 1 after an atomic purchase. Only a successful purchase deducts gems, adds the card, and increments the version.

Return all request status codes followed by the final version, five final gem balances, and five owned-card counts, all in [B,W,G,R,Y] order.

Function

processPurchases(gems: int[], cards: int[][], requests: int[][]) → int[]

Examples

Example 1

gems = [3,3,0,0,0]cards = [[0,2,1,0,0,0],[1,2,2,0,0,0]]requests = [[0,0],[0,1],[1,1]]return = [1,-1,1,2,0,0,0,0,0,1,1,0,0,0]

The first purchase succeeds and advances the version to 1. The stale second request conflicts. The last request uses the blue-card discount and succeeds.

Example 2

gems = [0,0,0,0,0]cards = [[4,1,0,0,0,0]]requests = [[0,0]]return = [0,0,0,0,0,0,0,0,0,0,0,0]

The card is unaffordable, so every part of the player state remains unchanged.

Constraints

gems.length = 5 and 0 <= gems[c] <= 10^9.
1 <= cards.length, requests.length <= 10^5.
Every card row has six integers; its reward color and every request card index are valid.
Every base cost is between 0 and 10^9.
Every expected version is between 0 and the number of requests.