Generate random String without repeating in swift - swift

Question

I want the function to generate random String without repeating.
For example this function maybe will print: ABCC
func randomString(length:Int) -> String {
let charSet = "ABCDEF"
var c = charSet.characters.map { String($0) }
var s:String = ""
for _ in (1...length) {
s.append(c[Int(arc4random()) % c.count])
}
return s
} print(randomString(length: 4))
and i want print random unique string only, E.g : ABCD

Answer 1

import GameplayKit
func randomString(length : Int) -> String {
let charSet = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters)
let shuffled = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: charSet) as! [Character]
let array = shuffled.prefix(length)
return String(array)
}
print(randomString(length: 4))

Answer 2

func randomString(length: Int) -> String {
let charSet = "ABCDEF"
var charSetArray = charSet.characters.map { String($0) }
var randArray: [String] = []
while charSetArray.count > 0 {
let i = Int(arc4random_uniform(UInt32(charSetArray.count)))
randArray.append(charSetArray[i])
charSetArray.remove(at: i)
}
var output: String = ""
for i in 0..<length {
output.append(randArray[i])
}
return output
}

Answer 3

How to use:
let randomString = "ABCDEF".random(length: 3)!
The return value is optional because the length might exceed the length of provided string.
Check out the full implementation:
import UIKit
import PlaygroundSupport
extension MutableCollection where Indices.Iterator.Element == Index {
mutating func shuffle() {
let c = count
guard c > 1 else { return }
for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) {
let d: IndexDistance = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
guard d != 0 else { continue }
let i = index(firstUnshuffled, offsetBy: d)
swap(&self[firstUnshuffled], &self[i])
}
}
}
extension Sequence {
func shuffled() -> [Iterator.Element] {
var result = Array(self)
result.shuffle()
return result
}
}
extension String {
func random(length: Int) -> String? {
let uniqueCharacters = Array(Set(characters.map({ String($0) })))
guard length <= uniqueCharacters.count else { return nil }
guard length > 0 else { return nil }
return uniqueCharacters[0..<length].shuffled().joined()
}
}