Reverse an array of integers without using Swift's object properties/methods

Question

At a last iOS Developer job interview I got a task that I didn't quite know how to do properly.

Task: Reverse an array of integers in place.

Inputs: arr (the array), and n - which is the number of elements in arr

Allocate as little memory as possible, and don't use Swift's object properties (so basically anything you access with a dot notation e.g .reverse(), .insert(at: etc. is not allowed)

Hint: what will be the new index for an element that was located at index `0`? What will be the index for an element located at index `n`? index `1`? — Willem Van Onsem, Jun 16 '19 at 10:58
Hint 2: you can swap the values of two variables `a` and `b` using tuple assignment: `(a, b) = (b, a)`. — vacawama, Jun 16 '19 at 11:12

Damiaan Dufaux · Accepted Answer · 2019-06-16T11:23:05.200

With tuples

func reverse(array: inout [Int], count: Int) {
    if count < 2 { return }
    var first = 0
    var last = count - 1
    while first < last {
        (array[first], array[last]) = (array[last], array[first])
        first += 1
        last -= 1
    }
}

Without tuples

func reverse(array: inout [Int], count: Int) {
    func swapAt(_ firstIndex: Int, _ secondIndex: Int) {
        let firstValue = array[firstIndex]
        array[firstIndex] = array[secondIndex]
        array[secondIndex] = firstValue
    }

    if count < 2 { return }
    var first = 0
    var last = count - 1
    while first < last {
        swapAt(first, last)
        first += 1
        last -= 1
    }
}

Nice catch. I edited the code. – Damiaan Dufaux Jun 16 '19 at 11:22 — Damiaan Dufaux, Jun 16 '19 at 11:22

Reverse an array of integers without using Swift's object properties/methods

1 Answers1

With tuples

Without tuples