What are the main differences between an array and a set, and why should you choose an array in certain cases?

An array is an ordered collection of elements where the order matters and duplicates are allowed. A set is an unordered collection of unique elements where duplicates are automatically excluded.

Main differences:

• Order: Arrays preserve the order of insertion, sets do not.
• Uniqueness: Sets store only unique elements, arrays do not.
• Access: Elements in an array can be accessed by index, in a set — no.

Why choose an array:

• When the order of elements is important.
• When duplicates are needed.
• When fast access by index is required.

Example in Swift:

let array = [1, 2, 2, 3] // preserves order and duplicates
let set: Set = [1, 2, 2, 3] // stores only unique: 1, 2, 3