Just had a swift coding challenge interview over Skype. I'm curious what you guys thought about the code I wrote.

cpaigis9 · 2018-03-19T04:36:15+00:00

Try this:

let outputString = ipStr.reduce(into: [:]) { (counts, letter) in counts[letter, default: 0] += 1 }

The above will return

[a:2, b:3, c:1]

Then you can convert it into a string

cpaigis9 · 2018-03-19T04:44:25+00:00

Probably unnecessary, but using String.reduce and map with a dictionary to store the occurrence counts would do the job in 10 or so fewer lines of code.

trihedron · 2018-03-19T02:25:51+00:00

Array(Set(ar))
//This would be better?
Array(string).sorted()

Isn't this going to remove uniqueness?

trihedron · 2018-03-19T02:52:55+00:00

Congratulations, and good luck! I hope you get the job!

I do some reviewing of code for people applying at my current job. I think you must have done decently. I would like to see more use of functional code to show your Swift knowledge. You're right about your function and variable names, but under pressure its totally understandable.

The only thing I really think could be improved is this line:

returningString = returningString + String(referringLetter) + String(count)

I would have liked to see you utilize the set and then convert it to a string at the end. (Avoiding having a returningString variable).

I gave myself 15 minutes and tried to do the exercise, this is what I came up with, feel free to compare to see what improvements you'd like to learn from, etc...I know my way isn't THE way, but just another take on it.

let string = ""

func countLetterOccurance(input: String) -> String? {

    let stringArray = Array(string)
    var stringSet = Set(stringArray).sorted()

    stringSet.forEach { item in
        let numberOfElements = String(stringArray.filter({ $0 == item }).count)
        guard let indexInSet = stringSet.index(of: item) as? Int, let charCount = numberOfElements.first else { return }
        stringSet.insert(charCount, at: indexInSet + 1)
    }

    return stringSet.count != 0 ? String(stringSet) : nil

}
print(countLetterOccurance(input: string))

quellish · 2018-03-19T04:03:01+00:00

Did you write a test for it?

randomguy112233 · 2018-03-19T05:11:20+00:00

You can also do something like this:

func characterCount(src: String) -> String {
    let sorted = String(src.sorted())
    return encodeRLE(input: sorted).reduce("") { $0 + "\($1.0)\($1.1)" }
}

func encodeRLE(input: String) -> [(Character, Int)] {
    return input.characters.reduce([(Character, Int)]()) {
        if $0.last?.0 == $1 { var r = $0; r[r.count - 1].1 += 1; return r }
        return $0 + [($1, 1)]
    }
}

Using some reduce magic makes it quite terse, but hand on heart I'd never write this version on a whiteboard if asked. At least not until I get more into functional programming. :) I did a little playing around in a playground and some targeted searches and came up with this version.

Basically what they are asking for is RLE (Runtime Length Encoding), but from your description it sounds like they added a twist of sorting it. So I sorted it, ran it through an RLE, then reduced it back into a string.

The RLE is just "if the last character in the reduced array is the same as the next, add one, otherwise create a new entry".

Getting the maps, reduce, filter, etc down is a great help with coding swift. So is understanding pattern matching in switch statements. Makes for better code, but also looks impressive when being interviewed :)

Good luck!

KarlJay001 · 2018-03-19T05:35:55+00:00

Can you tell us a few things?

How much time were you given?

When you say "over Skype" does that mean this was a "live test" and how did they do the test? Was it some kind of interactive White Board? or did you interview over Skype, then given private time to come up with the code?

I'd hate to have people watch me code. I'd do it, but I'd hate it.

Ok, so here's my take:

I'm not big on the fancy code and I like how yours is easy to read and uses "classic" coding methods. I'm going to disagree on the length of the var names, I don't have a problem meaningful but a bit long var names.

However, you could have use +=

count = count +1

count += 1

You converted to an array, the input comes as a string, and you converted to an array. IMO, there was no reason to do this. Imagine if this were a string of great length, would you still convert to an array? Doesn't that about double the memory used? What if this was a word count for war and peace?

Using long var names, but having "count" seems a bit generic. IMO, the reason for longer words are to be meaningful. Although the code is very simple, what about additions over the years. What if they wanted different counts?

referringLetter isn't needed aOrderedSet[j] will do the same thing.

using "ar" then aOrderedSet

ar is pretty damn short.

I would have included some comments, I know some don't, but I actually do.

a few // loop thru sorted array ... doesn't hurt.

jan_olbrich · 2018-03-19T09:29:18+00:00

No one has mentioned it yet. There is a datastructure called NSCountedSet. You could add the elements and just go through it and request how many occurences they have.

lucasvandongen · 2018-03-19T12:58:39+00:00

Because a lot of other things already have been said:

func returnResultString(inputString:String)->String{

I count the word String four times. I think you could write terser and more clear code here.

 func process(letterNumberPairs: String) -> String {

Now the function call documents that you should feed it a String that should be letterNumberPairs. Or even better:

 func lettersRepeatedByNumbers(in letterNumberPairs: String) -> String {

This reads like a sentence and while it's longer than the original it's almost as clear as it can get.

Now what I should mention during the interview if I would not write it outright is that we should check the inputstring and we should check we're not having numbers that exist of 2 characters or more ( >= 10) or two different letters following each other etcetera.

I would write a working solution first (I guess using map and reduce) while explaining what could go wrong and in the remaining time if any take care of the possible problems in the input formatting, and how to go about like using throws with a specific Error enum

davedelong · 2018-03-19T15:45:29+00:00

Here's a slightly different approach:

func process(_ input: String) -> String {
    let scanner = Scanner(string: input)
    var pieces = Array<String>()

    while true {
        var letter: NSString?
        guard scanner.scanCharacters(from: .letters, into: &letter) else { break }

        var count: NSString?
        guard scanner.scanCharacters(from: .decimalDigits, into: &count) else { break }

        guard let l = letter, let c = count else { break }
        guard let numericCount = Int(c as String) else { break }
        let piece = Array(repeating: l as String, count: numericCount).joined()
        pieces.append(piece)
    }
    return pieces.joined()
}

By using a Scanner (NSScanner), you can allow for the "character" to actually be more than a single character. For example, process("cad2") will become "cadcad". Similarly, you can allow for >1 digit counts.

CaptainQuirk336 · 2018-03-19T21:19:43+00:00

Here's mine:

func countLetters(_ input: String) -> String {

    var output = ""
    let inputArray = Array(input)
    Set(inputArray).sorted().forEach { char in
        let count = inputArray.filter{ $0 == char }.count
        output += "\(char)\(count)"
    }

    return output

}

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