
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. 


PROC Swap(BYTE ARRAY tab INT i,j)
  BYTE tmp
 
  tmp=tab(i) tab(i)=tab(j) tab(j)=tmp
RETURN
 
BYTE FUNC QuickSelect(BYTE ARRAY tab INT count,index)
  INT px,i,j,k
  BYTE pv
 
  DO
    px=count/2
    pv=tab(px)
    Swap(tab,px,count-1)
 
    i=0
    FOR j=0 TO count-2
    DO
      IF tab(j)<pv THEN
        Swap(tab,i,j)
        i==+1
      FI
    OD
 
    IF i=index THEN
      RETURN (pv)
    ELSEIF i>index THEN
      ;left part of tab from 0 to i-1
      count=i
    ELSE
      Swap(tab,i,count-1)
      ;right part of tab from i+1 to count-1
      tab==+(i+1)
      count==-(i+1)
      index==-(i+1)
    FI
  OD
RETURN (0)
 
PROC Main()
  DEFINE COUNT="10"
  BYTE ARRAY data=[9 8 7 6 5 0 1 2 3 4],tab(COUNT)
  BYTE i,res
 
  FOR i=0 TO COUNT-1
  DO
    MoveBlock(tab,data,COUNT)
    res=QuickSelect(tab,COUNT,i)
    PrintB(res) Put(32)
  OD
RETURN