Why collection algorithms matter in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the first element in the array.

Swift

let numbers = [1, 2, 3, 4, 5]
let firstNumber = numbers.[1]

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Alast()

Bfirst()

Ccount

Dappend()

Attempts:

3 left

💡 Hint

Common Mistakes

Using last() returns the last element, not the first.

Using count returns the number of elements, not an element.

append() adds an element, it does not retrieve one.

The first() method returns the first element of the array.

2fill in blank

medium

Complete the code to filter numbers greater than 3.

Swift

let numbers = [1, 2, 3, 4, 5]
let filtered = numbers.filter { $0 [1] 3 }

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A>

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters numbers less than 3, not greater.

Using '==' filters only numbers equal to 3.

Using '<=' includes numbers less than or equal to 3.

The filter method keeps elements where the condition is true. Here, we want numbers greater than 3.

3fill in blank

hard

Fix the error in the code to sum all numbers in the array.

Swift

let numbers = [1, 2, 3, 4, 5]
let total = numbers.reduce(0, [1])

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A{ $1 * $0 }

B{ $0 / $1 }

C{ $0 - $1 }

D{ $0 + $1 }

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication changes the result.

Division can cause runtime errors if dividing by zero.

The reduce method combines all elements using the closure. To sum, add the accumulator and current value.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

Swift

let words = ["apple", "bat", "car", "door"]
let lengths = [String: Int](uniqueKeysWithValues: words.filter { $0.count [1] 3 }.map { ($0, $0.[2]) })

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A>

Bcount

Clength

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters shorter words, not longer.

Using 'length' is not a valid property in Swift strings.

Filter words with count greater than 3, then map each word to a tuple of (word, word.count).

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values greater than 2.

Swift

let data = ["one": 1, "two": 2, "three": 3]
let result = data.filter { $0.value [1] 2 }.mapKeys { $0.key.[2]() }.mapValues { $0.[3] }

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A>

Buppercased

Cdescription

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters values less than 2.

Using 'lowercased' converts keys to lowercase, not uppercase.

Using 'count' on values is invalid since values are Int.

Filter values greater than 2, convert keys to uppercase, and convert values to strings using description.