
Sorting Algorithm

This is a sorting algorithm.   It may be applied to a set of data in order to sort it.    
For comparing various sorts, see compare sorts.  
For other sorting algorithms,   see sorting algorithms,   or:

O(n logn) sorts
Heap sort |
Merge sort |
Patience sort |
Quick sort
O(n log2n) sorts
Shell Sort
O(n2) sorts
Bubble sort |
Cocktail sort |
Cocktail sort with shifting bounds |
Comb sort |
Cycle sort |
Gnome sort |
Insertion sort |
Selection sort |
Strand sort
other sorts
Bead sort |
Bogo sort |
Common sorted list |
Composite structures sort |
Custom comparator sort |
Counting sort |
Disjoint sublist sort |
External sort |
Jort sort |
Lexicographical sort |
Natural sorting |
Order by pair comparisons |
Order disjoint list items |
Order two numerical lists |
Object identifier (OID) sort |
Pancake sort |
Quickselect |
Permutation sort |
Radix sort |
Ranking methods |
Remove duplicate elements |
Sleep sort |
Stooge sort |
[Sort letters of a string] |
Three variable sort |
Topological sort |
Tree sort


Use the quickselect algorithm on the vector

 [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
To show the first, second, third, ... up to the tenth largest member of the vector, in order, here on this page.

 Note: Quicksort has a separate task. 


MyList := [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
Loop, 10
	Out .= Select(MyList, 1, MyList.MaxIndex(), A_Index) (A_Index = MyList.MaxIndex() ? "" : ", ")
MsgBox, % Out
return
 
Partition(List, Left, Right, PivotIndex) {
	PivotValue := List[PivotIndex]
	, Swap(List, pivotIndex, Right)
	, StoreIndex := Left
	, i := Left - 1
	Loop, % Right - Left
		if (List[j := i + A_Index] <= PivotValue)
			Swap(List, StoreIndex, j)
			, StoreIndex++
	Swap(List, Right, StoreIndex)
	return StoreIndex
}
 
Select(List, Left, Right, n) {
	if (Left = Right)
		return List[Left]
	Loop {
		PivotIndex := (Left + Right) // 2
		, PivotIndex := Partition(List, Left, Right, PivotIndex)
		if (n = PivotIndex)
			return List[n]
		else if (n < PivotIndex)
			Right := PivotIndex - 1
		else
			Left := PivotIndex + 1
	}
}
 
Swap(List, i1, i2) {
	t := List[i1]
	, List[i1] := List[i2]
	, List[i2] := t
}