
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. 


// version 1.1.2
 
const val MAX = Int.MAX_VALUE
val rand = java.util.Random()
 
fun partition(list:IntArray, left: Int, right:Int, pivotIndex: Int): Int {
    val pivotValue = list[pivotIndex]
    list[pivotIndex] = list[right]
    list[right] = pivotValue
    var storeIndex = left
    for (i in left until right) {
        if (list[i] < pivotValue) {
            val tmp = list[storeIndex]
            list[storeIndex] = list[i]
            list[i] = tmp
            storeIndex++
        }
    }
    val temp = list[right]
    list[right] = list[storeIndex]
    list[storeIndex] = temp
    return storeIndex
}
 
tailrec fun quickSelect(list: IntArray, left: Int, right: Int, k: Int): Int {
    if (left == right) return list[left]
    var pivotIndex = left + Math.floor((rand.nextInt(MAX) % (right - left + 1)).toDouble()).toInt()
    pivotIndex = partition(list, left, right, pivotIndex)
    if (k == pivotIndex)
        return list[k]
    else if (k < pivotIndex)
        return quickSelect(list, left, pivotIndex - 1, k)
    else
        return quickSelect(list, pivotIndex + 1, right, k)
}
 
fun main(args: Array<String>) {
    val list = intArrayOf(9, 8, 7, 6, 5, 0, 1, 2, 3, 4)
    val right = list.size - 1
    for (k in 0..9) {
        print(quickSelect(list, 0, right, k))
        if (k < 9) print(", ")
    }
    println()
}