questions4.md

Topics covered

• Struct / Class / Enum definitions
• Data Structures (instantiation, pros / cons, running time)
• Bonus: Delegates, ARC / Memory Management

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Question 1

Reverse a number

Example:

123 -> 321

Solution:

func reverse(num: Int) -> Int {
    let numStr = "\(num)"
    return Int(String(numStr.reversed()))!
}

print(reverse(num: 123))

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Question 2

Given an array of strings:

• we want only the strings that are greater than 3 characters long Of those, return a dictionary where the key represents the character and the value represents the count of the character across the array Bonus: Make and use a String extension called length()

Example:

let arr = ["a", "aa", "aaa", "aaaa"] -> ["a": 4]

Solution:

func charCount(arr: [String]) -> [Character:Int] {

    var charCount: [Character:Int] = [:]
    let str = arr.filter { $0.length() > 3 }.joined()

    for char in str.characters {
        if charCount[char] != nil {
            charCount[char] = charCount[char]! + 1
        } else {
            charCount[char] = 1
        }
    }
    return charCount
}

extension String {
    func length() -> Int {
        return self.characters.count
    }
}

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Question 3

Convert an array of Int into an array of String

Example:

let arr = [1, 2, 3, 4] -> ["1", "2", "3", "4"]

Solution:

func convert(arr: [Int]) -> [String] {
    return arr.map { "\($0)" }
}

print(convert(arr: [1,2,3,4]))

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