Merge Sort

mergeSort.swift

public func mergeSort<T: Comparable>(_ A : inout [T]) -> [T] {
    
    if A.count == 2 {
        
        if A[0] > A[1] { return [A[1], A[0]] } else {
            
            return [A[0], A[1]]
        }
        
    } else if A.count == 1 {
        
        return [A[0]]
    } else {
        
        var tt = Array(A.prefix(upTo: A.count/2))
        var yy = Array(A.suffix(from: A.count/2))
        
        let aa = mergeSort(&tt)
        let bb = mergeSort(&yy)
        
        return mergeSorted(a: aa, b: bb)
    }
}

public func mergeSorted<T: Comparable>(a: [T], b: [T]) -> [T] {
    
    var indexA: Int = 0
    var indexB: Int = 0
    
    
    var finished = false
    
    var result: [T] = []
    
    while finished == false {
        
        if indexA > a.count-1 { b.suffix(from: indexB).map { result.append($0) }; finished = true; break } else
            if indexB > b.count-1 { a.suffix(from: indexA).map { result.append($0) }; finished = true; break } else
                
                if a[indexA] < b[indexB] {
                    
                    result.append(a[indexA])
                    indexA = indexA + 1
                } else {
                    
                    result.append(b[indexB])
                    indexB = indexB + 1
        }
    }
    
    return result
}

var a: [Int] = [3,5,1,10, 3, 6, 22, 55, 33, 22]

mergeSort(&a)