Set creation and operations in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using sets?

Consider the following Swift code that creates and manipulates sets. What will be printed?

Swift

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

A [3, 4]

B [1, 2]

C [1, 2, 3, 4, 5, 6]

D [5, 6]

💡 Hint

Think about what the union operation does to two sets.

The union of two sets combines all unique elements from both sets. Here, setA and setB combined have elements 1, 2, 3, 4, 5, and 6. Sorting them gives [1, 2, 3, 4, 5, 6].

❓ Predict Output

intermediate

What does this Swift code print after set intersection?

Look at this Swift code that finds the intersection of two sets. What is the output?

Swift

let setX: Set<Int> = [10, 20, 30, 40]
let setY: Set<Int> = [30, 40, 50, 60]
let intersectionSet = setX.intersection(setY)
print(intersectionSet.sorted())

A [10, 20]

B []

C [50, 60]

D [30, 40]

💡 Hint

Intersection returns only elements common to both sets.

The intersection of setX and setY contains elements present in both sets, which are 30 and 40. Sorting them results in [30, 40].

❓ Predict Output

advanced

What is the output of this Swift code using symmetricDifference?

This Swift code uses symmetricDifference on two sets. What will be printed?

Swift

let set1: Set<Int> = [1, 2, 3, 4, 5]
let set2: Set<Int> = [4, 5, 6, 7]
let symDiff = set1.symmetricDifference(set2)
print(symDiff.sorted())

A [1, 2, 3, 6, 7]

B [4, 5]

C [1, 2, 3, 4, 5, 6, 7]

D [6, 7]

💡 Hint

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

The symmetric difference excludes elements common to both sets (4 and 5). So the result is [1, 2, 3, 6, 7].

❓ Predict Output

advanced

What is the count of elements after subtracting sets in Swift?

Given these two sets, what is the count of elements in the result after subtracting setB from setA?

Swift

let setA: Set<Int> = [100, 200, 300, 400, 500]
let setB: Set<Int> = [300, 400, 600]
let differenceSet = setA.subtracting(setB)
print(differenceSet.count)

A 2

B 3

C 4

D 5

💡 Hint

Subtracting removes elements of setB from setA.

Elements 300 and 400 are removed from setA. Remaining elements are 100, 200, and 500, so count is 3.

🧠 Conceptual

expert

Which Swift set operation produces this output?

You have two sets: setM = [2, 4, 6, 8] and setN = [1, 2, 3, 4]. Which operation on setM and setN produces the output [1, 3, 6, 8] when sorted?

A setM.union(setN).subtracting(setM.intersection(setN))

B setM.symmetricDifference(setN)

C setM.intersection(setN).union(setM.subtracting(setN))

D setM.subtracting(setN).union(setN.subtracting(setM))

💡 Hint

Think about how union, intersection, and subtracting combine to form symmetric difference.

Option A computes union minus intersection, which is the symmetric difference. The output is [1, 3, 6, 8].

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