Problems › JavaScript › monitoring
Decide each call against a rate limit
An API gateway allows a caller so many requests in any trailing window. Requests it turned away do not count towards the limit — otherwise a rejected burst would lock someone out forever.
- Timestamps are in seconds and arrive in the order the calls did.
- A call is allowed when the number of already-allowed calls with a timestamp strictly newer than (now - window) is below the cap.
- Rejected calls leave no trace.
- A cap of zero or less rejects everything.
- The answer is one decision per call, in the same order.
rateLimitDecisions(times: list<int>, windowSeconds: int, maxCalls: int) → list<bool>
Where you start
function rateLimitDecisions(times, windowSeconds, maxCalls) {
}Worked examples
| Call | Result |
|---|---|
rateLimitDecisions([0,1,2,3], 10, 3) | [true,true,true,false] |
rateLimitDecisions([0,1,2], 10, 1) | [true,false,false] |
rateLimitDecisions([0,10,20], 10, 1) | [true,true,true] |
rateLimitDecisions([0,1,1,12], 10, 2) | [true,true,false,true] |
Hint
Keep only the timestamps you allowed. For each new call, drop the ones that have aged out, then count what is left.
Reference solution in JavaScript
function rateLimitDecisions(times, windowSeconds, maxCalls) {
const allowed = [];
const result = [];
for (const t of times) {
while (allowed.length > 0 && allowed[0] <= t - windowSeconds) allowed.shift();
const ok = maxCalls > 0 && allowed.length < maxCalls;
if (ok) allowed.push(t);
result.push(ok);
}
return result;
}