Foundations — Chapter Quiz · Data Structures & Algorithms

Question 1

1

What is the Big-O time complexity of accessing an element by index in a JavaScript array?

AO(log n)BO(n)CO(1)DO(n²)

Arrays backed by contiguous memory (V8 packed arrays) support constant-time index access. No traversal is needed.

Question 2

2

Which best describes amortized O(1) for Array.push?

AEvery single push takes O(1) timeBOccasional O(n) resizes are spread over n operations, making the per-push average O(1)CPush is O(log n) because of internal sortingDPush is O(n) because the array is immutable

When the backing buffer fills up, the engine doubles the capacity and copies all elements — O(n). Spread over n pushes that cost leads to O(1) amortized per operation.

Question 3

3

What distinguishes a 'packed' array from a 'holey' array in V8?

APacked arrays have more than 100 elementsBPacked arrays have no gaps (no undefined holes); holey arrays doCHoley arrays store only primitivesDPacked arrays are read-only

V8 tracks array "elements kinds". A packed array (e.g. [1,2,3]) is stored as a fast C-array. Deleting an element or writing beyond the length creates holes that downgrade to a slower holey type.

Question 4

4

When calculating the space complexity of a recursive function with depth d, what is the minimum extra space used?

AO(1) — recursion uses no stack spaceBO(d) — each call frame occupies stack spaceCO(d²)DO(n) always

Each active call frame sits on the call stack. A recursion of depth d therefore uses O(d) auxiliary space, independent of the work done per frame.

Question 5

5

Which complexity class grows fastest for large n?

AO(n log n)BO(n²)CO(2ⁿ)DO(n³)

Exponential O(2ⁿ) dominates all polynomial classes. For n=40, 2⁴⁰ ≈ 10¹² while n³ = 64,000.

Question 6

6

In JavaScript, objects are passed by value, so mutating a parameter inside a function never affects the caller's object.

TTrueFFalse

Objects and arrays are passed by reference (technically "pass by value of the reference"). Mutating a property inside a function changes the caller's object.

Question 7

7

The notation that describes the exact tight bound on an algorithm's growth — neither just an upper nor just a lower bound — is called ___ notation.

Θ (Theta) notation gives a tight bound: the algorithm runs in at least c₁·f(n) and at most c₂·f(n) for all large n. O gives only an upper bound; Ω gives only a lower bound.

Question 8

8

Which of the following are common benchmarking pitfalls in Node.js? (Select all that apply)

Select all that apply.

ARunning only one iteration without warm-up lets JIT deoptimizations skew resultsBconsole.time has microsecond precision and is always accurateCV8 may optimize away dead code that produces no observable outputDGC pauses can inflate timing measurements unpredictably

Single runs without warm-up miss JIT compilation costs. V8 can eliminate unreachable or unused computations. GC pauses are non-deterministic and pollute measurements. console.time wraps Date.now() which has only millisecond resolution — not ideal for tight loops; performance.now() is better.

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