Scala Scala Collections 2

Question 1

What is a `Stream` (LazyList in Scala 2.13+) in Scala?

Accepted Answer

A lazily evaluated, potentially infinite list

Answer

A `LazyList` (formerly `Stream`) is a lazily evaluated sequence where elements are computed on demand, supporting infinite sequences.

Question 2

What is the difference between `Seq` and `IndexedSeq` in Scala?

Accepted Answer

IndexedSeq guarantees O(1) random access by index; Seq only guarantees sequential traversal

Answer

`IndexedSeq` extends `Seq` and guarantees efficient O(1) element access by index, while `Seq` only guarantees linear traversal.

Question 3

How do you convert a Scala Map's keys to a Set?

Accepted Answer

Both map.keySet and map.keys.toSet work

Answer

Both `map.keySet` (returns a `Set`) and `map.keys.toSet` produce a `Set` containing the map's keys in Scala.

Question 4

What does `distinct` do on a Scala Seq?

Accepted Answer

Returns only unique elements in their original order

Answer

`distinct` returns a new sequence with duplicate elements removed, preserving the order of first occurrence.

Question 5

What is a `Map` in Scala and how do you create one?

Accepted Answer

An immutable key-value store created with Map(key -> value)

Answer

A Scala `Map[K,V]` stores key-value pairs; the default `Map` is immutable and created with `Map(key -> value, ...)`.

Scala Practice Test