How to generate a 4 digit random number with unique digits?

Question

Like: 0123, 0913, 7612
Not like: 0000, 1333, 3499

Can it be done with arcRandom() in swift? Without array or loop?

Or If that impossible, how it be done with arcRandom() in any way ?

Ignore the computer. How would you do this if you just had a pencil and paper? What steps would you take? — Abizern, Oct 14 '15 at 22:12

score 7 · Answer 1 · edited May 23 '17 at 11:52

7

You just want to shuffle the digits and pick the number you want.

Start with Nate Cook's Fischer-Yates shuffle code.

// Start with the digits
let digits = 0...9

// Shuffle them
let shuffledDigits = digits.shuffle()

// Take the number of digits you would like
let fourDigits = shuffledDigits.prefix(4)

// Add them up with place values
let value = fourDigits.reduce(0) {
    $0*10 + $1
}

edited May 23 '17 at 11:52

Community

1
1

answered Oct 15 '15 at 00:15

Rob Napier

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Leo Dabus · Answer 2 · 2015-10-27T19:39:36.293

1

var fourUniqueDigits: String {
    var result = ""
    repeat {
        // create a string with up to 4 leading zeros with a random number 0...9999
        result = String(format:"%04d", arc4random_uniform(10000) )
        // generate another random number if the set of characters count is less than four
    } while Set<Character>(result.characters).count < 4
    return result    // ran 5 times
}

fourUniqueDigits  // "3501"
fourUniqueDigits  // "8095"
fourUniqueDigits  // "9054"
fourUniqueDigits  // "4728"
fourUniqueDigits  // "0856"

edited Oct 27 '15 at 19:39

answered Oct 15 '15 at 00:29

Leo Dabus

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This approach scales poorly as the number of digits gets larger. – Rob Napier Oct 15 '15 at 13:11
@RobNapier the OP is asking for a four digits. In my tests here it generates around 90 numbers to extract 45. But there is no bias with 0 first here – Leo Dabus Oct 15 '15 at 13:16
Yeah; I can't figure out why it biases towards a leading zero when n is larger. My first calculations on it suggest it shouldn't, but I never seen a non-zero-leading result with n=8 or n=9. – Rob Napier Oct 15 '15 at 13:17
1

There's no need for the intermediate `Array` BTW. You can build a `Set` from any `SequenceType`. – Rob Napier Oct 15 '15 at 13:18
By "n=8 or n=9" I mean "looking for an 8-digit or 9-digit number." A good algorithm here shouldn't be tied to exactly four digits if it can help it. On StackOverflow, people tend to re-use these answers for similar problems that may not be identical. – Rob Napier Oct 15 '15 at 13:19

score 0 · Answer 3 · answered Feb 28 '18 at 11:21

Swift Code - For Generation of 4 digit

It gives number between 1000 and 9999.

    func random() -> String {
    var result = ""
    repeat {
        result = String(format:"%04d", arc4random_uniform(10000) )
    } while result.count < 4 || Int(result)! < 1000
    print(result)
    return result    
}

Please Note - You can remove this Int(result)! < 1000 if you want numbers like this - 0123, 0913

How to generate a 4 digit random number with unique digits?

3 Answers3