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Quicksort in Swift gives error

I am writing Quick Sort using a higher order function in Swift, but it gives

error: 'Int' is not convertible to '[Int]'
return quickSort(array: lesser) + [pivot] + quickSort(array: greater)

Here is the code:

func quickSort(array: [Int]) -> [Int] {
    var array = array

    if array.isEmpty {return []}

    let pivot = array.remove(at: 0)
    let lesser = array.filter { $0 < pivot }
    let greater = array.filter { $0 >= pivot }

    return quickSort(array: lesser) + [pivot] + quickSort(array: greater)

}

There is an error in the last line.

+3


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2 answers


I can't tell you why this isn't working (I think it should), but I can tell you how to fix it.

Replace this

return quickSort(array: lesser) + [pivot] + quickSort(array: greater)


with this

return
    quickSort(array: lesser) as [Int] +
    [pivot] +
    quickSort(array: greater)
+3


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Indeed, the compiler gets confused with data types in a multi-operator formula, including the return type of the function it is currently compiling.

There are probably many ways to help the compiler. Here's one that isn't associated with a redundant type (the key makes the pivot an array [Int]):



func quickSort(array: [Int]) -> [Int] 
{
    if array.count < 2 { return array }

    let pivotValue = array.first!  
    let lesser     = array.filter{ $0 < pivotValue }
    let greater    = array.filter{ $0 > pivotValue }
    let pivot      = Array(repeating: pivotValue, 
                               count: array.count - lesser.count - greater.count) 

    return  quickSort(array:lesser) + pivot + quickSort(array:greater)
}
0


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