Knuth shuffle: Difference between revisions
→{{header|Swift}}
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=={{header|Swift}}==
Version that works in Swift 5.x and probably above. This version works for any mutable bidirectional collection although O(n) time complexity can only be guaranteed for a RandomAccessCollection where the index meets the Apple requirements for O(1) access to elements.
Also has the advantage that it implemented the algorithm as written at the top of this page i.e. it counts down from the end and picks the random element from the part of the array that has not yet been traversed.
<syntaxhighlight lang="swift">extension BidirectionalCollection where Self: MutableCollection
{
mutating func shuffleInPlace()
{
var index = self.index(before: self.endIndex)
while index != self.startIndex
{
// Note the use of ... below. This makes the current element eligible for being selected
let randomInt = Int.random(in: 0 ... self.distance(from: startIndex, to: index))
let randomIndex = self.index(startIndex, offsetBy: randomInt)
self.swapAt(index, randomIndex)
index = self.index(before: index)
}
}
}
var a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
a.shuffleInPlace()
print(a)
</syntaxhighlight>
{{out}}
<pre>[1, 5, 2, 7, 6, 0, 9, 8, 4, 3]</pre>
'''Simple version (any Swift version):''' Extend Array with shuffle methods; using arc4random_uniform from C stdlib:
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