How should I practice First Successful Concurrent API Result Before a Timeout?

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

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

First Successful Concurrent API Result Before a Timeout

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Problem statement

All backend calls start concurrently at time 0. Call i completes after latencies[i] milliseconds, succeeds exactly when succeeds[i] is true, and yields values[i].

Return the value of the successful call with the smallest completion time that finishes no later than the shared timeoutMs. If several successful calls finish together, choose the smaller input index. Return the empty string when no successful call finishes before the timeout.

Function

firstSuccessfulResult(latencies: int[], succeeds: boolean[], values: String[], timeoutMs: int) → String

Examples

Example 1

latencies = [120,40,75]succeeds = [true,false,true]values = ["slow","error","winner"]timeoutMs = 100return = "winner"

The call at 40 ms fails. The call at 75 ms is the first success before the timeout.

Example 2

latencies = [50,50,10]succeeds = [true,true,false]values = ["left","right","bad"]timeoutMs = 50return = "left"

The two successful calls tie at the inclusive timeout, so the smaller index wins.

Example 3

latencies = [5,90]succeeds = [false,true]values = ["x","y"]timeoutMs = 80return = ""

The early call fails and the successful call completes too late.

Constraints

1 <= latencies.length <= 100000.
succeeds.length = values.length = latencies.length.
0 <= latencies[i], timeoutMs <= 10^9.
Each value contains at most 200 visible ASCII characters.