Dutch national flag problem: Difference between revisions
Added Swift solution
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# ''Sort the balls in a way idiomatic to your language.'' Yup!
# ''Check the sorted balls are in the order of the Dutch national flag.'' Not checked beyond eyeballing - is there a db implementation that gets <tt>order by</tt> wrong??
=={{header|Swift}}==
<syntaxhighlight lang="swift">// Algorithm from https://en.wikipedia.org/wiki/Dutch_national_flag_problem
func partition3<T: Comparable>(_ a: inout [T], mid: T) {
var i = 0
var j = 0
var k = a.count - 1
while j <= k {
if a[j] < mid {
a.swapAt(i, j);
i += 1;
j += 1;
} else if a[j] > mid {
a.swapAt(j, k);
k -= 1;
} else {
j += 1;
}
}
}
func isSorted<T: Comparable>(_ a: [T]) -> Bool {
var i = 0
let n = a.count
while i + 1 < n {
if a[i] > a[i + 1] {
return false
}
i += 1
}
return true
}
enum Ball : CustomStringConvertible, Comparable {
case red
case white
case blue
var description : String {
switch self {
case .red: return "red"
case .white: return "white"
case .blue: return "blue"
}
}
}
var balls: [Ball] = [ Ball.red, Ball.white, Ball.blue,
Ball.red, Ball.white, Ball.blue,
Ball.red, Ball.white, Ball.blue]
balls.shuffle()
print("\(balls)")
print("Sorted: \(isSorted(balls))")
partition3(&balls, mid: Ball.white)
print("\(balls)")
print("Sorted: \(isSorted(balls))")</syntaxhighlight>
{{out}}
<pre>
[white, blue, red, red, white, blue, red, blue, white]
Sorted: false
[red, red, red, white, white, white, blue, blue, blue]
Sorted: true
</pre>
=={{header|Tcl}}==
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