Swift

Question 1

When to use a For loop or While loop?

Answer 1

For loop: when you know the number of iterations ahead of time.

While loop: when you don’t know the number of iterations ahead of time

Question 2

== VS ===

Answer 2

== tests for the Equatable protocol. ie does “abc” equal “abc”

=== tests for address matching. Do two instances of an object have the same address?

Question 3

break vs return

Answer 3

Break: will exit loop or switch

Return: will exit the function

Question 4

What’s the syntax for replacing an element in an array with another element?

Answer 4

array[x] = y

Question 5

What’s the syntax for assigning a value to a dictionary?

Answer 5

dictionary[x] = y

Question 6

How do you check if a dictionary contains a value?

Answer 6

• dict.keys.contains(key)
• if let value = dict[key]
• if dict[key] != nil

Question 7

How do you determine how many times you want to repeat an operation?

Answer 7

First ask: What data do i need to see? all of it? some of it?

start from base case and develop from there. Consider writing out options.

Question 8

How to iterate both index and value of an array?

Answer 8

for (index, value) in array.enumerated()

Question 9

How to iterate elements of a dictionary?

Answer 9

for (key, value) in dictionary

Question 10

How to cast from Int to String?

Answer 10

Int(string)

returns optional

Question 11

How to cast from string to array?

Answer 11

Array(string)

Question 12

How would you instantiate the absolute minimum as an Integer?

Answer 12

Int.min

Question 13

How would you instantiate the absolute max as an Integer?

Answer 13

Int.max

Question 14

How to return the greater of two values?

Answer 14

max(x,y)

Question 15

How to return the lesser of two values?

Answer 15

min(x,y)

Question 16

How to return a lowercase version of string?

Answer 16

string.lowercased()

this returns a new object!

Question 17

How would you break a sentence into an array of strings?

Answer 17

string.components(seperatedBy: “ “)

Question 18

How to return the prefix of an array?

Answer 18

array.prefix(count)

Question 19

How to join an array of strings?

Answer 19

array.joined(separator: “”)

Question 20

How to remove and return an element in an array?

Answer 20

array.remove(at: index)

Question 21

Are swift parameters passed in as variables or constants?

Answer 21

Constants

Question 22

What does inout do?

Answer 22

Allows you to modify an object in place, instead of returning a new object

Question 23

What syntax do you use to pass an argument as inout?

Answer 23

• func test(inout string: String)
• test(string: &string)

Question 24

How would you insert an element in an array?

Answer 24

array.insert(value, at: index)

Question 25

How to clean a string of non alpha characters?

Answer 25

string.filter { $0.isLetter }

Question 26

How to convert a string to an array?

Answer 26

let array = Array(string)

Question 27

What does the type Int32 do?

Answer 27

It stores an integer with a length of 32 bits. This is different than the Int type which stores the default system value, which could be 32 or 64.

Question 28

How to join an array of strings?

Answer 28

let result = array.joined(separator: "")

Question 29

What is the inout syntax for a func signature?

Answer 29

ie func reverseString(string: inout String)

Question 30

What is the syntax for getting the first N elements of an array?

Answer 30

array.prefix(n)

Question 31

How would you sort an array of this type? [[Int: Int]]

Answer 31

array.sort { $0.values.first! < $1.values.first! }

Question 32

What is the diff between Sort, Sorted, and Sorted(by: )

Answer 32

Sort: called in place Sorted: returns a copy Sorted(by: ): returns a copy, accepts `>` or `<` as an argument

Question 33

How to swap 2 values?

Answer 33

(a, b) = (b, a)

Question 34

What does the Continue keyword do?

Answer 34

Prevents a loop from iterating after entering an If block

Question 35

How do you calculate an exponent?

Answer 35

let result = pow(x,y)

Question 36

What type does pow(x,y) return and how do you use it?

Answer 36

It returns Decimal type and it should be converted to Int/Float by returning: Int(NSDecimalNumber(decimal: n))

Question 37

How do you pop the last element of an array?

Answer 37

- .removeLast() to remove it

Question 38

What's the syntax for set?

Answer 38

let set: Set = [1,2,3]

Question 39

What numbers will this iterate over? for index in 1...5

Answer 39

1,2,3,4,5

Question 40

How many times will this run? for i in 0..<4

Answer 40

4

Question 41

How do you get the length of an array?

Answer 41

array.count

Question 42

What is the syntax to perform a swap?

Answer 42

(a,b) = (b,a)

Question 43

How can you combine two strings?

Answer 43

stringA + stringB

Question 44

How would you iterate an array starting at index N?

Answer 44

for i in N...array.count

Question 45

How to create a Set in Swift?

Answer 45

let set: Set = [1,2,3]

Question 46

How can you check if a set contains a value?

Answer 46

set.contains(value)

Question 47

How to add an element to a Set?

Answer 47

set.insert(value)

Question 48

How to declare a function argument as mutable?

Answer 48

write inout before the type func sortColors(_ nums: inout [Int])

Question 49

What is the diff between .reverse() and .reversed() ?

Answer 49

.reveresed() returns new value .reverse() in place

Question 50

What does `continue` do in a loop?

Answer 50

skips an iteration of the loop

Question 51

What does `break` do in a loop?

Answer 51

ends the loop entirely

Question 52

What does `Fallthrough` do in a loop?

Answer 52

allows for a switch case to proceed to the next case

Question 53

How can you create N number of arrays without instantiating them manually?

Answer 53

var arrays: [[Int]] = [] let n = 5 for _ in 0..

Question 54

How can you create N number of arrays without instantiating them manually? Do NOT use a for loop

Answer 54

let n = 5 `var arrays = [[Int]](repeating: [1,2,3], count: n)`

Question 55

How to get absolute number in swift?

Answer 55

abs(n)

Question 56

What is the time complexity of `.count` ?

Answer 56

o(1) on an Array or any object that conforms to `Random Access Collection` o(n) on non RAC conforming objects

Question 57

How would you iterate an array starting at indexN while also having access to the array's element?

Answer 57

for element in array[1...]

Question 58

Whats the diff between readLine() and CommandLine.arguments?

Answer 58

- readLine() prompts the user for input - commandLine pulls in arguments that are passed in at runtime

Question 59

How would you access the last element of an array?

Answer 59

array.last

Question 60

How to access strings by index?

Answer 60

Convert to array let stringArray = string.map{ String($0) }

Question 61

Are strings an instance of Array?

Answer 61

No, they are an instance of Collection. They are a collection of characters

Question 62

What is the syntax to create a Set of Integers?

Answer 62

let set = Set()

Question 63

How to access tuple elements?

Answer 63

let tuple = (a,b) let a = tuple.0 let b = tuple.1

Question 64

Continue vs break

Answer 64

Continue skips an iteration break ends the loop

Question 65

How to slice array?

Answer 65

array[x...y]

Question 66

How to clear whitespace in Swift?

Answer 66

import Foundation string.trimmingCharacters(in: .whitespaces)

Question 67

What is the expected output after trimming whitespace on this string: let originalString = " Remove whitespaces "

Answer 67

Output: "Remove whitespaces"

Question 68

How to filter out non-alphanumeric chars?

Answer 68

let output = string.filter { $0.isLetter || $0.isNumber }

Question 69

How to get Int from pow() ?

Answer 69

let integer = Int(pow(Double(a), Double(b)))

Question 70

How to pop the first element in an array?

Answer 70

array.removeFirst()

Question 71

What will 0...5 print?

Answer 71

0,1,2,3,4,5

Question 72

What will 0..<5 print?

Answer 72

0,1,2,3,4

Question 73

What is the name of this range syntax: 0...5

Answer 73

closed

Question 74

What is the name of this range syntax 0..<5

Answer 74

half open

Question 75

let nums = [1,2,3] what does nums[0..<0]) return?

Answer 75

An empty array [ ]

Question 76

What numbers does this return? let array = [1,2,3,4,5] array[0...3]

Answer 76

1,2,3,4

Question 77

What numbers does this return? let array = [1,2,3,4,5] array[0..<3]

Answer 77

0,1,2,3

Question 78

Is this operator "..." inclusive or exclusive? ie array[0...array.count]

Answer 78

inclusive

Question 79

What will this return? let array = [1,2,3,4,5] array[0..

Answer 79

1,2,3,4,5

Question 80

What will this return? let array = [1,2,3,4,5] array[0...array.count]

Answer 80

Fatal, index out of range