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Checkpoint 5: Validation of my solution

Forums > 100 Days of SwiftUI

Hello! I'm seeking assistance to verify whether my solution for checkpoint 5 is accurate. Could you please review it and provide feedback?

Here's my code:

// Your input is:
//      let luckyNumbers = [7, 4, 38, 21, 16, 15, 12, 33, 31, 49]
// Your goal is to:
//      Filter out any numbers that are even
//      Sort the remaining integers in the array in an ascending order
//      Map them to strings in the format "7 is a lucky number"
//      Print the resulting array, one item per line
// You cannot use any temporary variables

let luckyNumbers = [7, 4, 38, 21, 16, 15, 12, 33, 31, 49]

let oddLuckyNumbers = luckyNumbers.filter { !$0.isMultiple(of: 2) }

let sortedOddLuckyNumbers = oddLuckyNumbers.sorted { $0 < $1 }

let mappedOddLuckyNumbers = sortedOddLuckyNumbers.map {
    "\($0) is a lucky number"

for i in mappedOddLuckyNumbers {


You missed one important bit. @twoStraws asks you to code without using temporary variables.
You used: oddLuckyNumbers, sortedOddLuckyNumbers, and mappedOddLuckyNumbers.

-40 points from Hufflepuff!

// You cannot use any temporary variables

Hint: The lesson here is that Swift is a functional language. The output of one function can form the input to another function.


Yes a part of checkpoint is

To chain these functions, use luckyNumbers.first { }.second { }, obviously putting the real function calls in there.


let myLuckyNumbers = luckyNumbers.filter { !$0.isMultiple(of: 2) }.sorted() // etc

or (still "inline" but can be easier to read)

let myLuckyNumbers = luckyNumbers
    .filter { !$0.isMultiple(of: 2) }
    // etc

So you nearly there.

PS You do not need to use .sorted { $0 < $1 } as .sorted() will sort Int from less to more


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I see. My sincerest apologies @Obelix as I didn't know that creating a new variable is still using a temporary variable. Thank you for the clarification.

Here's my updated code

let luckyNumbersToCheck = [7, 4, 38, 21, 16, 15, 12, 33, 31, 49]

let newLuckyNumbersToCheck = luckyNumbersToCheck
    .filter {
        !$0.isMultiple(of: 2)
    .map {
        "\($0) is a lucky number"


for i in newLuckyNumbersToCheck {

I have an additional question. Is newLuckyNumbersToCheck still considered as a temporary variable?

I've also removed the $0 < $1 just like what @NigelGee suggested.


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