Set

Initializing a Set

// initializing a Set
var babyNames: Set<String> = ["Kim", "Hua", "Bertie", "Esther"]
var cohorts: Set = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]

Combining Sets

update(with:_)

// update
var numbers: Set = [1, 2, 3, 4, 5]
var oldValue = numbers.update(with: 3) // 3
oldValue = numbers.update(with: -1) // nil

intersection()

// intersection
// common elements of two groups
let employeeOneProficientLanguages: Set = ["Java", "Kotlin", "C", "Python", "SQL", "Go", "Dart", "JavaScript"]
let employeeTwoProficientLanguages: Set = ["Swift", "Objective-C", "C", "Python", "JavaScript"]
let languagesInCommon = employeeOneProficientLanguages.intersection(employeeTwoProficientLanguages)
print(languagesInCommon) // ["C", "Python", "JavaScript"]

subtracting()

// subtract
let dsaTopicsToStudy: Set = ["Big O Notation", "String", "Array", "Dictionary", "Set", "Character", "CharacterSet", "Stack", "Queue", "Linked List"]
let topicsCompleted: Set = ["Big O Notation", "String", "Array", "Dictionary", "Linked List"]
let topicsRemaining = dsaTopicsToStudy.subtracting(topicsCompleted)
print(topicsRemaining) // ["Queue", "Stack", "CharacterSet", "Character", "Set"]

symmetricDifference()

// symmetricDifference
// genres we each uniquely know
let myGenres: Set = ["Soca", "Reggae", "Hip Hop", "Country", "Blues", "Jazz", "Funk", "Zouk"]
let yourGenres: Set = ["Hip Hop", "Reggae", "Folk", "Jazz", "Blues", "Hi-Life", "Techno", "House"]
let genresWeCanTeachEachOther: Set<String> = myGenres.symmetricDifference(yourGenres)
print(genresWeCanTeachEachOther)

Comparing Sets

• isSubset
• isStrictSubset
• isSuperset
• isStrictSuperset
• isDisjoint

Finding Elements

contains()

Reminder contains on a Set is much faster than on an array. On a Set the runtime is O(1) and on a array the runtime is O(n). This is all because the values in a Set is Hashable so lookup is constant.

let jobApplied: Set = ["Pandora", "Zoc Doc", "Bloomberg", "Instagram", "CNBC", "Goolge"]
if !jobApplied.contains("Apple") {
  print("Don't hesistate to apply, having a BS in Computer Science is not a requirement.")
}

allSatisfy(Element -> Bool)

let evenNumbers: Set = [2, 4, 6, 8, 10, 12]
let areAllEven = evenNumbers.allSatisfy { $0 % 2 == 0 }
print(areAllEven) // true

NSOrderedSet and NSMutableOrderedSet

NSOrderedSet is an Objective-C API and allows for maintaining the order of a Set. NSOrderedSet is immutable and items cannot be added to it.

If you wish to add or modity the items of an ordered set you can use its counterpart, NSMutableOrderedSet.

let dupes = [1,1,1,2,2,3,3,3,3,4,9,9]

let regularSet = Set(dupes)

print(regularSet) // [1, 3, 2, 4]

let orderedSet = NSOrderedSet(array: dupes)
print(orderedSet)

print("last value of ordered set is \(orderedSet[orderedSet.count - 1])") // output 4

// we cannot add to a NSOrderedSet b/c it's immutable

// in order to add to an ordered set we need to use NSMutableOrderedSet

var mutableOrderedSet = NSMutableOrderedSet(array: dupes) // NS => Next Step => Jobs started NS, macOS

mutableOrderedSet.add(10)

mutableOrderedSet.insert(11, at: 3)

print(mutableOrderedSet)

Challenges

Challenge 1 - Unique number of occurences

LeetCode

Challenge 2 - Contains duplicate

LeetCode

Challenge 3 - Destination City

LeetCode

Challenge 4 - Design HashSet

LeetCode

Challenge 5 - Pangram

HackerRank

Challenge 6 - First unique Character in a String

LeetCode

Challenge 7 - Unique email addresses

LeetCode

Resources

1. Apple documentation - Set
2. Apple documentation - NSOrderedSet
3. Apple documentation - NSMutableOrderedSet