Set creation and operations in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an empty set of integers.

Swift

var numbers: Set<Int> = [1]

Drag options to blanks, or click blank then click option'

A[]

B{}

CArray()

DSet()

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] creates an empty array, not a set.

Using curly braces {} is invalid syntax for sets in Swift.

In Swift, an empty set is created using Set(). Using [] creates an empty array, and {} is not valid syntax for an empty set.

2fill in blank

medium

Complete the code to create a set with the elements 1, 2, and 3.

Swift

let digits: Set<Int> = [1]

Drag options to blanks, or click blank then click option'

ASet(1, 2, 3)

BSet([1, 2, 3])

C[1, 2, 3]

D(1, 2, 3)

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to pass multiple arguments directly to Set initializer.

Using array literal without Set initializer.

To create a set with elements, you can pass an array to the Set initializer like Set([1, 2, 3]). Using just square brackets creates an array, and Set(1, 2, 3) is invalid syntax.

3fill in blank

hard

Fix the error in the code to check if two sets have any common elements.

Swift

let setA: Set<Int> = Set([1, 2, 3])
let setB: Set<Int> = Set([3, 4, 5])
let hasCommon = !setA.[1](setB).isEmpty

Drag options to blanks, or click blank then click option'

Aintersection

Bunion

CsymmetricDifference

Dsubtracting

Attempts:

3 left

💡 Hint

Common Mistakes

Using union returns all elements from both sets, not just common ones.

Using symmetricDifference returns elements in either set but not both.

The intersection method returns the common elements between two sets. Checking if this intersection is not empty tells us if they share any elements.

4fill in blank

hard

Fill both blanks to create a set of even numbers from 1 to 10.

Swift

let numbers = Set(1...10)
let evenNumbers = numbers.filter { $0 [1] 2 [2] 0 }

Drag options to blanks, or click blank then click option'

A%

B==

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes odd numbers to be selected.

Using '>' does not check for evenness.

To find even numbers, use the modulo operator % to check if the remainder when divided by 2 is zero.

5fill in blank

hard

Fill all three blanks to create a dictionary from a set of words with their lengths, but only include words longer than 3 characters.

Swift

let words: Set<String> = Set(["apple", "cat", "banana", "dog"])
let wordLengths = [[1]: [2] for [3] in words if [2] > 3]

Drag options to blanks, or click blank then click option'

Aword

Bword.count

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names.

Not filtering words by length.

We create a dictionary where keys are words and values are their lengths. We iterate over each word in the set and include only those with length greater than 3.

Practice

1. What is true about a Set in Swift?

easy

A. It can only store numbers, not strings.

B. It stores duplicate values in the order they were added.

C. It stores unique values without any specific order.

D. It always keeps elements sorted alphabetically.

Solution

1. Step 1: Understand Set properties

   A Set in Swift stores unique values and does not keep any order.

2. Step 2: Compare options with Set behavior

   It stores unique values without any specific order. matches the unique and unordered nature of Sets. Others describe arrays or sorted collections.

3. Final Answer:

   It stores unique values without any specific order. -> Option C

4. Quick Check:

   Set = unique + unordered [OK]

Hint: Remember: Sets never keep duplicates or order [OK]

Common Mistakes:

• Thinking Sets keep order like arrays
• Assuming Sets allow duplicates
• Believing Sets only store numbers

2. Which of the following is the correct way to create a Set of integers in Swift?

easy

A. let numbers = {1, 2, 3, 4} as Set<Int>

B. let numbers: Set<Int> = [1, 2, 3, 4]

C. let numbers = Set(1, 2, 3, 4)

D. let numbers = [1, 2, 3, 4] as Set

Solution

1. Step 1: Recall Set creation syntax

   In Swift, a Set can be created by specifying type and using square brackets with values.

2. Step 2: Check each option's syntax

   let numbers: Set<Int> = [1, 2, 3, 4] uses correct syntax: Set<Int> = [1, 2, 3, 4]. Others have syntax errors or wrong casting.

3. Final Answer:

   let numbers: Set<Int> = [1, 2, 3, 4] -> Option B

4. Quick Check:

   Set creation = type + brackets [OK]

Hint: Use Set<Type> with brackets for values [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Trying to cast arrays directly to Set without syntax
• Missing type declaration when needed

3. What will be the output of this Swift code?

let setA: Set<Int> = [1, 2, 3, 4]
let setB: Set<Int> = [3, 4, 5, 6]
let result = setA.intersection(setB)
print(result.sorted())

medium

A. [3, 4]

B. [1, 2]

C. [5, 6]

D. [1, 2, 3, 4, 5, 6]

Solution

1. Step 1: Understand intersection operation

   Intersection returns elements common to both sets. Here, common elements are 3 and 4.

2. Step 2: Check printed output

   Result is converted to a sorted array, so output is [3, 4].

3. Final Answer:

   [3, 4] -> Option A

4. Quick Check:

   Intersection = common elements [OK]

Hint: Intersection = only items in both sets [OK]

Common Mistakes:

• Confusing intersection with union
• Forgetting to sort before printing
• Expecting all elements combined

4. Identify the error in this Swift code snippet:

var fruits: Set<String> = ["apple", "banana", "orange"]
fruits.append("grape")

medium

A. The brackets [] cannot be used to create a Set.

B. You cannot add strings to a Set of strings.

C. The Set must be declared as a constant, not variable.

D. Sets do not have an append method.

Solution

1. Step 1: Check Set modification methods

   Sets use insert() to add elements, not append().

2. Step 2: Analyze the code error

   Calling append() on a Set causes a compile error because it is not defined for Set.

3. Final Answer:

   Sets do not have an append method. -> Option D

4. Quick Check:

   Use insert() to add to Set [OK]

Hint: Use insert(), not append(), to add Set items [OK]

Common Mistakes:

• Using append() instead of insert()
• Thinking Sets are immutable by default
• Confusing array and Set methods

5. Given two sets:

let setX: Set<Int> = [1, 2, 3, 4, 5]
let setY: Set<Int> = [4, 5, 6, 7]

Which Swift code correctly creates a new set containing elements in either setX or setY but not in both?

hard

A. let result = setX.symmetricDifference(setY)

B. let result = setX.union(setY)

C. let result = setX.intersection(setY)

D. let result = setX.subtracting(setY)

Solution

1. Step 1: Understand symmetricDifference

   Symmetric difference returns elements in either set but not in both.

2. Step 2: Compare with other operations

   Union combines all elements, intersection finds common, subtracting removes elements of second from first.

3. Final Answer:

   let result = setX.symmetricDifference(setY) -> Option A

4. Quick Check:

   Symmetric difference = exclusive elements [OK]

Hint: SymmetricDifference = items in one set only [OK]

Common Mistakes:

• Using union instead of symmetricDifference
• Confusing intersection with symmetricDifference
• Using subtracting which is one-sided