A list of helpful methods and syntax to reference before coding challenges and whiteboard interviews.

Download: SwiftCheatsheet.playground

Last update on 2020-09-22 for Swift 5.1

String

• string.map { $0 } // Convert String to Character array
• s[s.index(s.startIndex, offsetBy: i)] // Character at "i"
• s[s.index(s.startIndex, offsetBy: i)..<s.index(s.startIndex, offsetBy: i + length)] // substring of length at "i"
• string.contains(char) // Bool check
• String(string.sorted()) // alphabetized string

Array / Stack / Queue

• var array = [Int]()
• var array = Array(repeating: 0, count: n) //array of size n
• array.append(item) // add to end
• array.firstIndex(of: item) // index (Swift5)
• array.remove(at: index)
• array.compactMap { $0 } // remove nils
• array.reduce([], +) // combine arrays

Set

• var set = Set() // needs to be var to allow insert
• Set(array) // cast array to set
• set.insert(item)
• let itemOptional = set.remove(item)
• set.contains(item)

Dictionary / Map (HashMap)

• var map = [String: String]()
• map["foo"] = "bar" // insert and overwrite
• let optionalValue = map["foo"] // get (nil if doesn't exist)
• map["foo"] == nil // check if key exists
• map["foo"] = nil // removes a key
• map.forEach { print($0.value) } // prints each value stored

Loops

• for item in array
• while condition {}
• repeat {} while condition

Enums

• guard case let .enumType(property) = enumInstance else { return }
// let property = enumInstance(property)
• if case .enumType = enumInstance { ... }
• if case 1...100 = num { ... } // if 1 <= num && num <= 100

Math

• min(a, b)
• max(a, b)
• NSDecimalNumber(decimal: pow(x, y)).intValue //x^y
• abs(num) // absolute value

Data / File

• let file = Bundle.main.path(forResource: "filename", ofType: "ext") // load filename.ext from project
• let data = try? String(contentsOfFile: file) // extract data from file
• let classInstance = JSONDecoder().decode(ClassName.self, from: data) // json data into class
• let string = String(data: data, encoding: .utf8) // data into string
• let data = string.data(using: .utf8) // string into data