Heap Sort Swift

HeapSort.swift

//Safe bounds check for Array
//http://stackoverflow.com/questions/25329186/safe-bounds-checked-array-lookup-in-swift-through-optional-bindings
extension Collection {
    /// Returns the element at the specified index iff it is within bounds, otherwise nil.
    subscript (safe index: Index) -> Iterator.Element? {
        return index >= startIndex && index < endIndex ? self[index] : nil
    }
}

//Helper function to exchange position in one array
//From: http://stackoverflow.com/questions/24077880/swift-make-method-parameter-mutable
func exchange<T>(_ data: inout [T], i:Int, j:Int) {
    let temp:T = data[i]
    data[i] = data[j]
    data[j] = temp
}

//Heap Sort methods
func leftLeafIndex(_ rootIndex:Int)->Int{
    let heapIndex = rootIndex+1
    return heapIndex*2-1
}

func rightLeafIndex(_ rootIndex:Int)->Int{
    let heapIndex = rootIndex+1
    return heapIndex*2
}

func heapLastIndex<T:Comparable>(_ A:Array<T>)->Int{
    return A.count-1
}

func parentOfNode<T:Comparable>(_ A:Array<T>, indexNode:Int)->Int{
    return indexNode/2
}

func maxHeapify<T:Comparable>(_ A:inout Array<T>,indexRoot:Int){
    if leftLeafIndex(indexRoot)>heapLastIndex(A) {return}
    let rootValue = A[indexRoot] as T
    var largestIndex = indexRoot
    var largestValue = rootValue
    
    if let leftLeafValue:T = A[safe:leftLeafIndex(indexRoot)] {
        if leftLeafValue > largestValue {
            largestValue = leftLeafValue
            largestIndex = leftLeafIndex(indexRoot)
        }
    }
    
    if let rightLeafValue:T = A[safe:rightLeafIndex(indexRoot)] {
        if rightLeafValue > largestValue {
            largestValue = rightLeafValue
            largestIndex = rightLeafIndex(indexRoot)
        }
    }
    
    
    if largestIndex != indexRoot {
        exchange(&A, i: indexRoot, j: largestIndex)
        maxHeapify(&A,indexRoot: largestIndex)
    }}

func buildMaxHeap<T:Comparable>(_ A:inout Array<T>){
    if A.count<2 {return}
    var lastParentIndex:Int = A.count/2
    while lastParentIndex >= 0 {
        maxHeapify(&A, indexRoot: lastParentIndex)
        lastParentIndex -= 1;
    }
    
}

func heapSort<T:Comparable>(_ A:Array<T>)->Array<T>{
    var A = A
    if A.count<2 {return A}
    buildMaxHeap(&A)
    var sortedA:Array<T> = []
    while A.count>1 {
        sortedA.insert(A[0], at: 0)
        exchange(&A, i: 0, j: A.count-1)
        A.removeLast()
        maxHeapify(&A, indexRoot: 0)
    }
    sortedA.insert(A[0], at: 0)
    return sortedA
}

// Heap Sort MAX-Priority Queue
func maxNode<T:Comparable>(_ A:Array<T>)->T{
    return A[0]
}

func extractMaxNode<T:Comparable>(_ A:inout Array<T>)->T{
    let max = A[0]
    A[0] = A[A.count-1]
    A.removeLast()
    maxHeapify(&A, indexRoot: 0)
    return max
}

func increaseNode<T:Comparable>(_ A:inout Array<T>, index:Int, value:T){
    var index = index
    if A[index] > value {return}
    A[index] = value
    while (index >= 0 && A[parentOfNode(A,indexNode: index)]<value){
        exchange(&A, i: index, j: parentOfNode(A, indexNode: index))
        index = parentOfNode(A, indexNode: index)
    }
}

func insertNode<T:Comparable>(_ A:inout Array<T>, value:T){
    A.append(value)
    increaseNode(&A, index: A.count-1, value: value)
}

//Main
var unsortedArray2:Array<Int> = [4,1,3,2,16,9,10,14,8]
print("Unsorted array :" + unsortedArray2.description)

let sortedArray2 = heapSort(unsortedArray2)
print("Sorted array with heap sort :" + sortedArray2.description)

Why don't you use "swap" function?