Zip for combining sequences in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using zip?

Consider the following Swift code that uses zip to combine two arrays. What will be printed?

Swift

let numbers = [1, 2, 3]
let words = ["one", "two", "three"]
for (number, word) in zip(numbers, words) {
    print("\(number): \(word)")
}

A one: 1\ntwo: 2\nthree: 3

B 1: one\n2: two

C 3: three\n2: two\n1: one

D 1: one\n2: two\n3: three

💡 Hint

Remember that zip pairs elements from both sequences in order.

The zip function pairs elements from numbers and words by their positions. So the first pair is (1, "one"), second is (2, "two"), and third is (3, "three"). The loop prints each pair in order.

❓ Predict Output

intermediate

What happens when zipping sequences of different lengths?

What will be the output of this Swift code?

Swift

let a = [10, 20, 30, 40]
let b = ["a", "b"]
for (num, letter) in zip(a, b) {
    print("\(num)\(letter)")
}

A 10a\n20b

B 10a\n20b\n30c\n40d

C 30c\n40d

D 10a\n20b\n30\n40

💡 Hint

Think about how zip handles sequences of different lengths.

The zip function stops when the shortest sequence ends. Here, b has only 2 elements, so only two pairs are formed.

🔧 Debug

advanced

Why does this Swift code using zip cause a runtime error?

Examine the code below. Why does it cause a runtime error?

Swift

let nums = [1, 2, 3]
let words = ["one", "two"]
let zipped = zip(nums, words)
let array = Array(zipped)
print(array[2])

A Type error because zipped is not convertible to Array

B Syntax error because zip requires sequences of equal length

C Index out of range error at runtime because zipped has only 2 elements

D No error, prints (3, "three")

💡 Hint

Check how many elements zipped contains and what index is accessed.

The zip pairs only up to the shortest sequence length, so zipped has 2 elements. Accessing array[2] causes an index out of range runtime error.

🧠 Conceptual

advanced

What is the type of the result of zip in Swift?

Given two arrays a and b, what is the type of zip(a, b) in Swift?

A Sequence<(Int, String)>

B Zip2Sequence<Array<Int>, Array<String>>

C [(Int, String)]

D Array<(Int, String)>

💡 Hint

Think about what zip returns before converting to an array.

The zip function returns a Zip2Sequence type that lazily pairs elements from the two sequences. It is not an array until converted.

🚀 Application

expert

How to sum pairs of numbers using zip in Swift?

You have two arrays of integers: arr1 and arr2. You want to create a new array where each element is the sum of the corresponding elements from arr1 and arr2. Which code snippet correctly does this using zip?

A let sums = zip(arr1, arr2).map { (a, b) in a + b }

B let sums = zip(arr1, arr2).map { $0 + $1 }

C let sums = zip(arr1, arr2).map { $0 * $1 }

D let sums = arr1.enumerated().map { $0.element + arr2[$0.offset] }

💡 Hint

Remember the closure syntax for map when using zip.

Option A correctly uses zip to pair elements and a closure with two parameters to sum them. Option A is incorrect because $0 is a tuple, so $0 + $1 is invalid. Option A works but does not use zip. Option A multiplies instead of sums.